When I walked away from my four-year marriage, many years ago, friends and family members wanted to know why I would leave what they had believed to be a happy marriage. That wasn’t an easy question to answer, not for me and especially not for the man I was leaving.

The hard-to-explain truth for me was that I knew the marriage was over when his car pulled into the driveway at the end of the day and I thought: Oh God, is he home already?

And the sad truth for him was that I needed to leave so that I could be happy.

This explanation didn’t satisfy the people we knew and they started to encourage me to confide in them that I was having an affair. I was not, and never had been, but I realized that infidelity, for them, would have been a much easier explanation for the divorce. So easy, in fact, that I wouldn’t be surprised to find out that my soon-to-be ex-husband had resorted to using this as the excuse.

Infidelity happens fairly frequently in marriages (although not in the majority), which has driven a common perception that infidelity is a major cause of divorce. In researching the chapter on infidelity for my new book, however, I read dozens of articles that try to find proof that this is the case in more than a small minority of break-ups and evidence simply does not exist.

Before we get the most recent evidence on this topic, let me give you an example that explains why this research is so difficult.

Consider two hypothetical people, Jane and John, who were married for a few years when John decided that he no longer wished to be married to Jane. In this case John felt lonely and neglected, but it doesn’t really matter why he wanted to leave, and so he began to look for love outside of their marriage. He eventually found it and one difficult night he told Jane that he was leaving her for another women. She was heart broken, of course, but there was nothing she could do.

A few years later both Jane and John are invited to participate in an online survey of why marriages end. As part of the survey they are asked: “What is the number one reason your marriage ended?” Jane honestly responds that infidelity ended her marriage and John honestly responds that a lack of love was the cause.

Now imagine that thousands of people exactly like John and Jane take this survey. In some cases the woman had searched for love outside of the marriage, and in some cases it was the man. But in every case the one who left told the researcher that the marriage ended because they were unhappy and the one who was left told the researcher that the marriage ended because of infidelity.

What does this (hypothetical) study find? That 50% of all marriages ended because of infidelity. But of course, for this particular group of people that conclusion would be inaccurate – all the marriage ended because one person in the relationship decided to find their way out of an unhappy marriage.

A new paper, by researchers in Norway, addresses this issue and finds that despite the perception that infidelity is a leading cause of breakup (from either marriage or a cohabitating relationship) they find little evidence that this is the case.

Many people (6 out of every 10) in this survey admitted to having engaged in some form of infidelity at some point in their lives. In most of those cases, however, the infidelity did not involve sexual intercourse – the majority reported having fallen in love with another person (30%) or having kissed another person (32%) without further sexual contact while in a committed relationship.

Among both men and women below the age of 50 (which is the age group that experiences the highest level of martial infidelity), infidelity does not appear among the top three causes of relationship break-up. Those are: lost love (47%), quarrelling (30%) and boredom (29%). (Participants could give up to three reasons.)

They do find that infidelity is among the top four reasons men and women over the age of 50 have experienced a break-up, along with lost love (tied with infidelity at 38%) and “other” and quarrelling (tied with 27% each). But even that result doesn’t prove that infidelity is the direct cause of relationship dissolution. It simply says that older men and women are reluctant to leave an existing relationship until the have secured a new partner; an unsurprising result given how difficult it can be to find love in later stages of life.

Psychologists Denise Previti and Paul Amato provide the most convincing evidence that infidelity is not a direct cause of divorce using couple-specific data collected over seventeen years. Their research concludes that men and women who are already likely to divorce are more likely to have had sex outside of their marriage; infidelity in is the consequence, not the direct cause, of an already unhappy marriage.

I am not so naïve to believe that sometimes people cheat in happy marriages and that cheating causes an otherwise healthy relationship to dissolve. But saying that infidelity is an important cause of divorce is like saying that heart failure kills the majority of people – all of our hearts stop when we die, but most the time that is because the person is too ill to live on.

I want to sincerely thank Vicki Larson (@OMGchronicles) for sending me this new research.


Træen, Bente and Frode Thuen (2013). “Relationship problems and extradyadic romantic and sexual activity in a web-sample of Norwegian men and women.” Forthcoming in the Scandinavian Journal of Psychology.

Previti, Denise, and Paul R. Amato. “Is Infidelity a Cause or a Consequence of Poor Marital Quality?” Journal of Social and Personal Relationships 21, no. 2 (2004): 217–230.