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  • Those who cheated in one relationship had three times the odds of cheating in their next one, per a new study. Tweet This
  • On average, norms about fidelity and commitment levels are higher for marriage than other relationships. Tweet This

If someone cheats on their partner in one relationship, what are the odds they will do so in another relationship? That’s the question addressed in a new study published in the Archives of Sexual Behavior,1 titled “Once a Cheater, Always a Cheater? Serial Infidelity Across Subsequent Relationships.” The researchers found that those who were unfaithful in one relationship had three times the odds of being unfaithful in the next relationship, compared to those who had not been unfaithful in the first one. Let’s look deeper.

This research was conducted by a team from our lab at the University of Denver; the study was headed up by Kayla Knopp along with colleagues Shelby Scott, Lane Ritchie, Galena Rhoades, Howard Markman, and yours truly. It used our national sample of individuals first recruited when aged 18 to 34, who were in unmarried, serious, romantic relationships.2 Thus, while most of the literature on infidelity focuses on marriage, this new study focused on those mostly at pre-marriage stages of life. That is one of the advances from this work but not the only one. The other is that the sample and methods allowed for assessing infidelity across two relationships within the context of this longitudinal sample that followed individuals for five years, focusing on their romantic relationships.

Historical Findings

There is an extensive literature on infidelity in married relationships with a growing literature on what is often called extra-dyadic sexual involvement (ESI) in unmarried relationships. The literature on infidelity inside and outside of marriage is well summarized in the new paper. I will describe a few highlights here.3

An overwhelming majority of people have the expectation of fidelity of sexual and, often, emotional connection in monogamous relationships. That is especially obvious in marriage, but it’s also true in serious, unmarried relationships. Sure, there have always been some who seek “open” relationships, where partners agree that it is okay to have sex outside the relationship under some conditions, but that is not very common.

While the lifetime risks for infidelity in marriage have generally run around 20%,4 rates of sex with someone outside a current relationship are much higher among those who are unmarried.5 This should not be shocking since both the norms about fidelity as well as average commitment levels are higher for marriage than other relationships, on average. The possibility of fidelity is simply not as high for those who have not settled down to make a long-term (or lifetime) commitment to a particular partner. Nevertheless, while people may not have settled down to committing to another for the long haul, they tend to expect faithfulness.6

Knopp and colleagues note some of the most common risk factors for infidelity based on prior research. Those include:

  • Low commitment to the present relationship
  • Low or declining relationship satisfaction
  • Accepting attitudes about sexual relations outside the relationship
  • Attachment insecurity: both avoidant and anxious
  • Differences in individual levels of sexual inhibition and excitement
  • Being a man versus a woman, though this may be changing.

Those findings are mostly from the literature on marriage with some findings from unmarried relationships. If you want a deeper review of factors associated with greater odds of cheating in unmarried relationships, I wrote about that subject here and here based on an earlier study drawing from the same project sample as the new study. The new study does not focus on predictors of infidelity but on the likelihood that it will be repeated, and it uses particularly strong methods for doing so.

Following People Through Two Relationships

Most studies of infidelity are retrospective and cross-sectional, focusing at single points while asking about present and past relationships.7 To my knowledge, this new study is unique because people were followed in real time (or close to it) from one relationship into the next, completing comprehensive surveys about their relationships at each time point during the longitudinal method. Contrast that with a method where, for example, you asked a sample of middle-aged people if they had ever had sex outside of one or more relationships in their past. That would be a different study, and, while interesting, would be subject to retrospective bias. People are believed to remember things better—and typically to report them more accurately—when asked closer in time to when those events occurred. That’s what Knopp and colleagues did.

For the new study, the overall national sample from the project started with 1,294 individuals. However, the analyses for this new study had to be based on those who were surveyed across two relationships over the course of the five years that the sample was followed. That means that only those who had broken up from one relationship and then entered another during that period would be analyzed. That left 484 individuals. If you are used to studies in sociology with thousands of people, that may seem like a smallish sample, but for the questions addressed here, it’s large and more than sufficient.

The average duration of the first relationships was 38.8 months while the average duration of the second was 29.6 months. Thus, the relationships studied were mostly serious and of substantial duration. No one was married at the start of the project but some would have married that first partner or the second during the time frame of the study. For the most part, however, it is best to think about these findings in the context of the stage of life where people are often seriously involved but not yet married—a stage of life that has grown substantially in the past few decades.

At each time point (which tended to be every four to six months), participants were asked, “Have you had sexual relations with someone other than your partner since you began seriously dating?” In this project, participants were also asked if they had either known or suspected their present partner of having sex with someone else. Obviously, there are biases when people are self-reporting such behavior. That’s a problem for the whole literature. Further, the specific questions used in this study may exclude emotional affairs as well as some online affairs where there is some sexual aspect but the respondent tells themselves they are not actually having sex. Also, in such a sample there would be some small percentage of people who would have been in some sort of consensual non-monogamous arrangement, where having sex with someone outside the relationship would be the same thing as cheating because there was some agreement about this. Knopp and colleagues note that there is no way with this data set to isolate such relationships, but there are strong reasons to believe that such open relationships are a very small percentage in the overall sample.

Knopp and colleagues controlled for some of the variables known to be associated with greater and lower risk of being unfaithful, net of other factors like relationship quality and commitment to one’s partner. That is, the study controlled for age, gender, socioeconomic status, and race.

Then and Again

Forty-four percent (44%) of this sample reported having had sex with someone other than their present partner in one or both of the relationships studied. Further, 30% reported that they knew at least one of the partners in the two relationships had cheated on them. That seems to me like quite a bit of infidelity in these unmarried relationships. Nevertheless, keep in mind that this is not a good estimate of the odds that someone will be unfaithful in an unmarried relationship. To be in this sample, a person would have had to have broken up in at least one serious relationship and entered another. Thus, this result does not mean that 44% of those under 40 in the U. S. have been unfaithful to a partner, and it certainly does not mean that such a high percentage who are married in a similar age range have or will be unfaithful. Getting that percentage measured correctly would require a different type of sample and method to yield the best estimate of how likely it is that people will have cheated on any partner before eventually settling down in marriage among those who have married. Closely related to that question, Galena Rhoades and I found in a previous study that 16% of those followed into marriage in the study’s parent project described here reported that they had cheated on their eventual spouse sometime before marriage.8

In this new study, 45% of those who reported cheating on their partner in the first relationship reported also doing so in their second. Among those who had not cheated in the first, far less, 18%, cheated in the second. While the odds of cheating on a partner were far greater if one had done so in the past, it is also true that a person cheating in one relationship was not destined to do so in the next relationship. In fact, slightly more people who had cheated in the first relationship studied did not report cheating in the second.

The study also found that those who were certain that their partner in the first relationship had cheated were twice as likely as those not reporting this to experience a cheating partner in the second relationship. Again, history was not destiny, but history did speak to greater odds of a repeat experience.


It would be incorrect to assume that one is destined to endlessly repeat painful relationship patterns. And yet, some people are at much greater risk than others for negative outcomes in romantic relationships (and marriage), and they are at greater risk for repeat experiences. Some people are simply more likely than others to cheat on their partners and more likely to choose partners who cheat on them and to do so in more than one relationship. This touches on the complex subject of selection into risk, which Galena Rhoades and I have written about more than a few times (for example, here and here).

The study described here was not designed to address complicated questions such as how the risk of infidelity might be lowered in relationships and marriage, or how it could be prevented from happening again. Future research could examine what predicts whether or not someone who cheated on one partner does so again; however, most of the same predictors of ever cheating will predict repeatedly cheating quite well. Among all of the factors associated with cheating, some are surely more amenable to change than others. Variables that are biological (e.g., differences in proneness to sexual excitement) or cultural (and thus impacting individual values) are in the mix, but so are other factors, like commitment, that I believe people have some control over.

Galena Rhoades and I have described how relationship histories may play an important and causal role in eventual relationship quality in marriage (or not in marriage, for that matter). Specifically, while having more experience in various aspects of life is usually a good thing, having more experience in relationships may not be so good when those experiences include serious involvements that alter one’s odds of succeeding in finding and keeping lasting love. Nevertheless, behaviors of the past do not have to be the definition of one’s future.

Scott M. Stanley is a research professor at the University of Denver and fellow of the Institute for Family Studies.

Editor's Note: The views and opinions expressed in this article are those of the author and do not necessarily reflect the official policy or views of the Institute for Family Studies.

1. Knopp, K., Scott, S.B., Ritchie, L.L., Rhoades, G.K., Markman, H.J., & Stanley, S.M. (2017). Once a cheater, always a cheater? Serial infidelity across subsequent relationshipsArchives of Sexual Behavior. Advance online publication. https://doi.org/10.1007/s10508-017-1018-1

2. The Relationship Development Study. For a description of the sample and basic methods, see Rhoades, G. K., Stanley, S. M., & Markman, H. J. (2010). Should I stay or should I go? Predicting dating relationship stability from four aspects of commitment. Journal of Family Psychology, 24(5), 543-550.

3. Since the literature is so well cited in the recent paper (and in papers cited in the recent paper), I will make no attempt here to cite each point regarding prior findings in this piece.

4. Allen, E. S., Atkins, D., Baucom, D. H., Snyder, D., Gordon, K. C., & Glass, S. P. (2005). Intrapersonal, interpersonal, and contextual factors in engaging in and responding to extramarital involvement. Clinical Psychology: Science and Practice, 12, 101-130.

5. Treas, J., & Giesen, D. (2000). Sexual infidelity among married and cohabiting Americans. Journal of Marriage and the Family, 62, 48–60.

6. Maddox Shaw, A. M., Rhoades, G. K., Allen, E. S., Stanley, S. M., & Markman, H. J. (2013). Predictors of extradyadic sexual involvement in unmarried opposite-sex relationships. Journal of Sex Research, 50(6), 598 - 610. DOI:10.1080/00224499.2012.666816

7. There are also a few studies that look at what factors earlier in following a longitudinal sample predict eventual infidelity, e.g.: Previti, D., & Amato, P.R. (2004). Is infidelity a cause or a consequence of poor marital quality? Journal of Social and Personal Relationships, 21, 217–230.; Allen, E. S., Rhoades, G. K., Stanley, S. M., Markman, H. J., Williams, T., Melton, J., & Clements, M. L. (2008). Premarital precursors of marital infidelity. Family Process, 47, 243-259.

8. Rhoades, G. K., & Stanley, S. M. (2014). Before “I Do”: What do premarital experiences have to do with marital quality among today’s young adults? Charlottesville, VA: National Marriage Project.