Why do people cheat when they are happy in their relationship?
The short answer
Unhappiness does predict infidelity, but weakly. In the best prospective study, lower satisfaction raised the odds by a small margin, and most people who were dissatisfied did not cheat. Much of what predicts infidelity sits in the individual rather than in the couple. That is a pattern across populations, and it cannot tell you what happened in your own relationship.
What readers think
When someone cheats, is the relationship usually the reason?
Anonymous. One vote per reader.
This question usually arrives with a specific person attached to it. Either you have just found out and the part that will not fit is that you thought things were fine, or you are the one who did it and cannot produce the grievance that would make it make sense.
The folk account says infidelity is a symptom. Something was missing, so someone went looking. It is tidy, and it has one large problem. When researchers measure how satisfied people are and then wait to see who cheats, satisfaction turns out to be a genuine predictor and a weak one.
Satisfaction predicts it, and not by much
The most informative design here is prospective: measure people first, then wait. One study followed 993 unmarried adults in opposite-sex relationships, surveying them every four months for twenty months[1]. Over that window, 14.2% reported sexual involvement with someone outside the relationship, and the gender gap was small, at 15.0% of men and 13.8% of women.
Lower relationship satisfaction at the start did predict who went on to do it. The odds ratio was 0.82, meaning each step up the satisfaction scale shaved a modest slice off the odds. Lower dedication to the relationship behaved similarly, at 0.83. Larger effects came from elsewhere: hostile communication, having a partner who had themselves been unfaithful, and problematic drinking. Across the whole set, the standardised differences between those who did and did not go on to cheat stayed within roughly a third of a standard deviation.
Two things did not predict it at all. How often the couple had sex, and how dissatisfied people were with their sex life. That is worth holding onto, because it contradicts one of the most confident things people say about this.
Much of what predicts it sits in the person, not the couple
A separate line of work compares three kinds of predictor directly: who someone is demographically, what their relationship is like, and what their sexual disposition is. One study of 506 men and 412 women in monogamous heterosexual relationships found that 23.2% of men and 19.2% of women reported having cheated during their current relationship[2].
What came out on top was neither the demographics nor, for men, the relationship. How readily someone becomes sexually aroused, and the particular pattern of what does and does not inhibit them, predicted infidelity for both sexes. Relationship happiness and compatibility in sexual attitudes predicted it for women, and did not enter the picture for men at all. Marital status and religiosity, the two variables people reach for first, mattered less than either.
The number that deserves the most attention is the one about what was left over. Everything measured, taken together, accounted for about 17% of the variation among men and 21% among women. Four fifths of it is unexplained. Anyone who tells you they know why people cheat is describing a slice of a picture that is mostly still blank.
What people say when you ask them their own reasons
Asking people directly produces a more crowded answer than the folk theory expects. Research that put 495 people's stated reasons through a statistical sorting found eight distinct motives rather than one or two[3]: anger, self-esteem, having fallen out of love, low commitment, feeling neglected, sexual desire, wanting sexual variety, and situational factors such as being drunk or away from home. Only some of those describe something wrong with the relationship. Wanting variety and being in a particular situation are not deficits, and they did not reduce to the motives that are. The traits that went with them differed too: comfort with sex outside a committed attachment tracked the variety motive, while attachment insecurity tracked anger, neglect and lost love.
The sharpest version of the finding comes from a study of people who were actively seeking affairs, recruited through a website built for the purpose[4]. They reported high satisfaction with the affairs and little moral regret, and relationship satisfaction, intimacy and conflict did not predict who had them. Sexual dissatisfaction did, which is a direct contradiction of the prospective study above and should be reported as one rather than smoothed over.
If you are reading this because it happened to you
The reason this evidence is worth having is narrow and real. The inference most people make within about an hour of finding out is: they cheated, so I must have been failing them, and I need to work out how. That inference does not follow from anything the research shows. At the level of populations, dissatisfaction is a weak signal, most unhappy people never cheat, and a substantial share of those who do describe their relationships as fine. The premise of the self-audit is not well supported.
What the evidence cannot do is tell you about your relationship. A weak association across thousands of people is perfectly compatible with your particular case being exactly what the folk theory describes. Population data removes an assumption. It does not supply a verdict, and anyone offering you one from a study is overreaching.
It is also worth separating two questions that arrive fused together. Why did this happen, and whose fault is it. People usually ask the first while meaning the second, and the answers are not the same shape.
It depends, on what?
What changes the answer
Two conclusions get pulled out of this that the evidence will not carry.
The first is that infidelity is never really about the relationship. That is not what the numbers say. Lower satisfaction, lower dedication and hostile communication all predicted later infidelity in the prospective work, in the direction everyone expects. Weak is not zero, and some affairs are exactly what they look like.
The second is the mirror image: that because the effect is small, nothing anyone does makes any difference. A small average effect across a population says very little about any single couple. It is entirely consistent with the relationship having been the whole story in one case and irrelevant in the next.
The limitation underneath all of it deserves stating plainly rather than as a footnote. Nearly every figure here comes from people reporting on their own conduct, in surveys, about something they have powerful reasons to hide from a partner and some reason to hide from a researcher. Under-reporting is close to certain, and there is no reason to think it is spread evenly. Most designs are cross-sectional, so they photograph both things at once and cannot say which came first. The one prospective study ran for twenty months among unmarried young adults, which is a narrow window onto something that plays out across decades of marriage. The people recruited through an affair website are about as self-selected a group as exists, were mostly men in their fifties, and cannot stand in for anyone else. Treat every percentage in this answer as an estimate with wide and largely unmeasured error around it.
Where people disagree
Both sides of it
Reasonable people land in different places on this. Here is the strongest version of each case, not a straw man of the one we disagree with.
The case for yes
- In the strongest prospective evidence available, relationship satisfaction predicted later infidelity only weakly, and the overwhelming majority of dissatisfied people did not cheat.
- Individual characteristics, including sexual arousability and problematic drinking, predicted infidelity as strongly as or more strongly than anything measured about the couple.
- When people are asked their own reasons, several of the motives that emerge, including wanting variety and simply being in a particular situation, do not describe a relationship deficit at all.
- Among people actively pursuing affairs, overall relationship quality did not predict who had them, which is difficult to reconcile with a pure symptom account.
The case for no
- The same prospective study did find lower satisfaction, lower dedication and hostile communication predicting infidelity, in the expected direction. The pattern is real, just smaller than folk theory assumes.
- Self-report about one's own motives is a weak instrument. Someone who cheated has obvious reasons to describe the relationship as fine, and may not have reliable access to their reasons in any case.
- A single global satisfaction rating is coarse. It can miss a specific and serious problem, and it says nothing about what the months before actually felt like.
- The most striking evidence that happy people cheat comes from users of a site built for arranging affairs, a group so self-selected that generalising from it to ordinary relationships is not defensible.
Evidence
What the research says
- Moderate evidence993 individuals followed for 20 months
In a prospective study of 993 unmarried adults surveyed every four months for twenty months, 14.2% reported sexual involvement outside the relationship. Lower baseline satisfaction predicted it with an odds ratio of 0.82 and lower dedication with 0.83, while frequency of sex and sexual dissatisfaction did not predict it at all.
Shaw, A. M., Rhoades, G. K., Allen, E. S., Stanley, S. M., & Markman, H. J., Predictors of Extradyadic Sexual Involvement in Unmarried Opposite-Sex Relationships (2013)(opens in a new tab)What this does not show
Participants were unmarried and mostly in their mid-twenties, so the findings do not transfer cleanly to long marriages. The outcome relied on single-item self-report about a behaviour people conceal, and twenty months is a short observation window. Predictors were measured once at baseline, so the study cannot capture a relationship that deteriorated during the follow-up.
- Moderate evidence506 men and 412 women
Among 506 men and 412 women in monogamous heterosexual relationships, 23.2% of men and 19.2% of women reported cheating during their current relationship. Sexual arousability and inhibition patterns predicted infidelity for both sexes, while relationship happiness and sexual-attitude compatibility predicted it for women only. The full model explained 17% of the variance for men and 21% for women.
Mark, K. P., Janssen, E., & Milhausen, R. R., Infidelity in Heterosexual Couples: Demographic, Interpersonal, and Personality-Related Predictors of Extradyadic Sex (2011)(opens in a new tab)What this does not show
Cross-sectional, so it cannot separate cause from consequence: an unhappy relationship might precede the infidelity or follow it. The sample was recruited online and skews young and Western, and the outcome depended on people volunteering that they had cheated. The unexplained four fifths of variance is the honest headline and is rarely quoted alongside the rest.
- Limited evidence495 participants, mostly young adults
When 495 people's stated reasons for infidelity were analysed statistically, eight distinct motives emerged, including several that do not describe a relationship deficit, such as wanting sexual variety and situational factors. The authors framed this as evidence against treating infidelity purely as a symptom of relationship problems.
Selterman, D., Garcia, J. R., & Tsapelas, I., Motivations for Extradyadic Infidelity Revisited (2019)(opens in a new tab)What this does not show
Retrospective self-report of one's own motives, gathered mostly from young adults with an average age around twenty, which is a poor basis for generalising to married people. Stated motives are reconstructions offered after the fact and may describe how someone has come to explain the behaviour rather than what drove it.
- Limited evidenceRoughly 800 respondents at each of two time points
In surveys of roughly 800 users of a website built for arranging affairs, relationship satisfaction, intimacy and conflict did not predict who pursued them, and participants reported high satisfaction with the affairs and little regret. Sexual dissatisfaction was the exception and did predict involvement.
Selterman, D., Joel, S., & Dale, V., No Remorse: Sexual Infidelity Is Not Clearly Linked with Relationship Satisfaction or Well-Being in Ashley Madison Users (2023)(opens in a new tab)What this does not show
The most self-selected sample in this answer by a wide margin: people who paid to join a service for this purpose, mostly men with an average age in the early fifties. It establishes that satisfied people pursuing affairs exist and are not rare within this group, and nothing about how common that is elsewhere. Its finding on sexual dissatisfaction directly contradicts the prospective study, which is unresolved.
How we rate evidence strength
- Strong evidence
- Multiple independent studies, including replications or meta-analyses, point the same way.
- Moderate evidence
- Several studies support this, but samples are limited or findings vary by population.
- Limited evidence
- Early, small, or single-study evidence. Treat this as a reasonable hypothesis, not a settled fact.
- Contested
- Credible researchers disagree, or the evidence points in conflicting directions.
Comparative view
Different perspectives
Traditions and disciplines answer this differently. We describe what each one teaches. We are not telling you which is right, and no tradition speaks with a single voice.
What the Evidence Can and Cannot Settle
The methodological situation is worth stating in its own right. Almost all of this literature is cross-sectional self-report on a behaviour that carries real social and legal consequences in some places, which means the measurement instrument is a person deciding whether to tell you. Randomised designs are impossible for obvious reasons. Prospective studies are the strongest tool available and there are very few of them, they run for short periods, and they mostly follow young unmarried people because that is who stays reachable for follow-up. Where two well-conducted studies disagree, as they do here on whether sexual dissatisfaction matters, the honest position is that the question is open rather than that one of them has settled it.
Therapist Perspective
Practitioners who see couples after a disclosure often describe the search for a cause as a task the betrayed partner takes on with enormous energy and little return. The account they arrive at tends to say more about what they can bear to believe than about what happened. A common clinical move is to shift the question from why to how: not what was lacking, but what the sequence of small permissions looked like, since people rarely decide to have an affair in one step. Practitioners also report that a partner insisting nothing was wrong and a partner insisting everything was wrong are both, often, describing a real thing incompletely. All of this is what clinicians report from the room, not something a trial has established.
Not a settled view
Clinical traditions differ sharply here. Approaches drawn from systems thinking treat an affair as arising from the couple as a unit, while trauma-informed practitioners argue that framing invites blame onto the betrayed partner and should be kept well away from the early work.
Secular Perspective
Read in secular terms, explanation and justification come apart quite sharply. Knowing that a behaviour has weak relationship-level predictors and stronger individual-level ones is a claim about causes, and it establishes nothing about responsibility. A person who acted on an impulse they did not choose to have still chose what to do about it, and adult moral accounting generally runs on the second thing rather than the first. This framing also treats the absence of a satisfying explanation as tolerable. Not every significant event in a life has a cause proportionate to its consequences, and demanding one can keep someone stuck longer than accepting that it may not exist.
Islamic Perspective
Islamic ethics has a well developed account of wrongdoing that does not require the wrongdoer to have been deprived of anything. The self inclined toward what it desires, and temptation acted on despite knowing better, are standard categories in the tradition, and they sit comfortably with the idea that a person in a good marriage might still do this. Scholars have long counselled guarding the circumstances that make transgression easy rather than assuming that a satisfied person is safe from it. At the same time the tradition places real obligations on both spouses regarding each other's emotional and physical needs, so a reading that removes the relationship from the picture entirely would not be faithful to it either. What is set out here is the shape of that tradition's argument, not a ruling aimed at anyone reading it.
Not a settled view
Contemporary Muslim counsellors differ over how much weight to put on marital neglect when advising a couple after infidelity, with some treating it as essential context and others warning that raising it early functions in practice as blame directed at the wronged spouse.
Practical steps
What you can actually do
Separate the question of why it happened from the question of whose fault it is. They arrive fused and they have different answers, which is why the conversation about them goes in circles.
Treat your partner's account of their own reasons as one account rather than as evidence. It is worth hearing. It was produced under pressure by someone with an interest in how it lands, and it is not a finding.
If you have started auditing your own conduct for the failure that caused this, put a limit on it. The premise is not well supported by the evidence and the search has no natural stopping point.
Be equally careful with the opposite move. Deciding it had nothing to do with the relationship can become its own way of avoiding a conversation worth having.
If you are the one who did it, saying you were happy and do not know why is an honest answer and not a sufficient one. What is usually needed is not a cause but an account of how the decision actually got made, step by step.
Worth unlearning
Common misconceptions
That infidelity is reliable evidence something was wrong. It is weak evidence, and a substantial share of people who cheat describe their relationships as satisfying.
That happy people cheating means the relationship never matters. Relationship variables did predict infidelity prospectively; they simply did so with small effects.
That research findings can tell you about your own case. They describe rates across populations, and a weak population-level association is compatible with almost any individual story.
That the prevalence figures are precise. Rates move a great deal with sample and question wording, and while the direction of the reporting error is known, its size is not.
That there is one reason people cheat. When motives are measured directly they separate into distinct clusters that do not collapse into each other.
The short version
Key takeaways
Lower relationship satisfaction did predict later infidelity in prospective research, with an odds ratio of 0.82, which is real but small.
ResearchIndividual characteristics such as sexual arousability and heavy drinking predicted infidelity at least as strongly as anything measured about the couple.
ResearchA model containing everything researchers measured explained roughly a fifth of who cheated, leaving most of it unaccounted for.
ResearchThe evidence undercuts the assumption that you must have failed somehow. It cannot tell you whether you did.
By definition
Worth saying
When to get professional help
Seeing someone on your own is worth doing if hunting for the explanation has become what your days are organised around: reconstructing timelines, going back through months of your own behaviour looking for the point where you failed. That pattern is very common after discovery, it tends not to lift on its own, and part of why is that the question it chases often has no findable answer.
Couples counselling is a separate decision and a reasonable one if both of you want to understand what happened. It helps to be honest with a counsellor at the outset about whether you are there to work something out or to decide something, because those are different pieces of work.
If someone is controlling your movements, your money or who you are allowed to see, or if you have been threatened, that belongs with a domestic abuse service before it belongs with any relationship counsellor.
Still wondering
Related questions people ask
No. It means you cannot infer that it did from the fact that it happened. Relationship factors do predict infidelity, just weakly on average. Whether they were operating in your case is a separate question that no study can answer for you.
Community
What other people say
These are readers describing their own relationships, not professionals. Take them as experience, not advice, and please do not name anyone.
No one has shared their experience yet. If you have been here, you would be the first, and probably the most useful thing on this page.
Check our work
Sources
- [1]Predictors of Extradyadic Sexual Involvement in Unmarried Opposite-Sex Relationships(opens in a new tab)
Shaw, A. M., Rhoades, G. K., Allen, E. S., Stanley, S. M., & Markman, H. J. · The Journal of Sex Research · 2013
- [2]Infidelity in Heterosexual Couples: Demographic, Interpersonal, and Personality-Related Predictors of Extradyadic Sex(opens in a new tab)
Mark, K. P., Janssen, E., & Milhausen, R. R. · Archives of Sexual Behavior · 2011
- [3]Motivations for Extradyadic Infidelity Revisited(opens in a new tab)
Selterman, D., Garcia, J. R., & Tsapelas, I. · The Journal of Sex Research · 2019
- [4]No Remorse: Sexual Infidelity Is Not Clearly Linked with Relationship Satisfaction or Well-Being in Ashley Madison Users(opens in a new tab)
Selterman, D., Joel, S., & Dale, V. · Archives of Sexual Behavior · 2023