Is "Once A Cheater, Always A Cheater" Really True?

UPDATE: This story has been updated to reflect the study author's comments.

While there's no real way to accurately predict whether or not a person will cheat on their partner, the old adage "once a cheater, always a cheater" exists for a reason. But is it really true?

Well, a new study published in the Archives of Sexual Behavior has found some evidence for truth to that anecdotal belief.

Every couple has different definitions of what counts as cheating, but for the study, researchers examined what they called "extra-dyadic sexual involvement" (ESI), or having sexual relations with someone other than a partner.

Researchers followed 484 unmarried people (329 women and 155 men) who had been in at least two relationships over the course of five years, seeking insight on whether or not having engaged in infidelity once made a person more likely to do it again. The participants selected were all in relationships with someone of the opposite sex, though researchers say that they hope to study same-gender couples in the future.

"The goal of the study was to look at the impact of cohabitation on marital outcomes, and at the time the study began, gay marriage wasn’t legalised nationally," Kayla Knopp, MA, lead author of the study, tells Refinery29.

Participants were asked to complete surveys by mail every 4 to 6 months for 5 years, and were asked to answer questions such as, "Have you had sexual relations with someone other than your partner since you began seriously dating?"

The results?

Those who already had a history of engaging in ESI behaviour were three times as likely to report cheating again in another relationship. They also found that those who had been cheated on in the past were more likely to figure out if their subsequent partners were cheating.

"The takeaway for us is that we all need to pay attention to our romantic pasts in order to make better choices for our future (or current) relationships," Knopp says. "These results suggest that if someone has struggled to stay faithful in the past, they should do some personal work to figure out why the infidelity happened so they can avoid repeating those patterns in the future. And if someone has been with an unfaithful partner in the past, they may want to pay close attention to red flags in their future relationships so they can avoid ending up in that situation again."

The researchers acknowledged that ESI may not encompass all behaviors that couples think of as infidelity, and some couples (such as those in open relationships) may not think of ESI as cheating. So while ESI is "probably accurately labeled as cheating," we won't know for sure if this applies to the average couple. Plus, it's important to note that 484 people is a relatively small sample size, and cheating is of course an extremely complex issue.

That being said, the research does provide some interesting insight into the likelihood that someone who has cheated before will cheat again — just take it with a healthy dose of skepticism and the knowledge that a person's past doesn't always indicate what they'll do in the future.