Someone who cheats on a long-term romantic partner before marriage is three times more likely to cheat in a later relationship than is one who stayed true, according to new research from the University of Denver.

The study, "Once a Cheater, Always a Cheater? Serial Infidelity Across Subsequent Relationships," looked at infidelity in one relationship as a risk factor for infidelity in a subsequent relationship. It was recently published in the Archives of Sexual Behavior.

The researchers used a national sample of individuals who had been recruited for the study when they were between the ages 18 and 34. Unlike most studies on infidelity, the subjects were all initially unmarried, but in serious romantic relationships. The research followed them through two romantic relationships.

What happens in nonmarital relationships is important, they wrote, "given that most people in the U.S. have multiple dating relationships before entering into a marriage or long-term commitment with a partner and research suggests that individuals' earlier romantic experiences may have consequences that can persist into later relationships or marriage."

The study didn't just examine the habits of a serial cheater. Researchers also found that those who had been cheated on were twice as likely to report the same cheating behavior from their next partner. And those who suspected their previous-relationship partner of cheating on them were four times more likely to say they were suspicious of subsequent partners than those who did not believe they'd been cheated on.

As for infidelity, "it's not like it's certain to happen, but the odds are much greater," said Scott Stanley, a research professor in the University of Denver's psychology department and one of the study authors.

The study

Of those who cheated in the first relationship, 45 percent went on to cheat in the second relationship, compared to 18 percent that didn't cheat in the first relationship, but did so in the second.

Neither gender nor marital status changed the link between infidelity in the first relationship and in the second.

In background information, the authors noted previous research that shows the "vast majority" of romantic relationships expect monogamy, married or not. While infidelity is widespread (an estimated 1 in 5 for married couples and as many as 7 in 10 for unmarried couples), they wrote that infidelity is "usually damaging" for both parties and hard on relationships. It's one of the most often-cited causes of divorce.

They also noted risk factors for infidelity, including low levels of commitment to the relationship, declining satisfaction in the relationship, permissive attitudes about cheating, changing social norms, as well as personality traits of those who cheat.

In the University of Denver study, first relationships lasted an average of 38.8 months before they ended, while second relationships had endured an average of 29.6 months by study's end. Sixty-five percent of participants said they lived with their first-relationship partner at some point (married or not), while 19 percent reported that living arrangement with their second relationship.

Still a taboo

Studies have shown that American care somewhat less about cohabiting than they did in the past. Attitudes have changed some on nonmarital births, as well. But infidelity's fan base has not grown significantly.

"An overwhelming majority of people have the expectation of fidelity of sexual and, often, emotional connection in monogamous relationships," Stanley wrote on an Institute for Family Studies blog about the new findings. "This is especially obvious in marriage, but it's also true in serious, unmarried relationships. Sure, there have always been those who seek 'open' relationships where partners agree that it is OK to have sex outside the relationship under some conditions, but that is not very common."

He notes that commitment levels are higher for married relationships than for others. But the majority in a relationship expect their partner to be faithful.

For example, a 2014 Gallup poll placed cheating on a spouse "dead last" in acceptable behaviors behind abortion, cohabitation, nonmarital births, divorce and pornography, among others. Just 6 percent said adultery is "acceptable."

In 2016, experts said that about one-third of couples who try to patch things up following infidelity succeed in doing so over the long term.

University of Utah sociologist Nicholas Wolfinger recently documented what he calls a "generation gap" since 2000 when it comes to infidelity: "Older Americans cheat more than in the past. Younger Americans cheat less," according to his findings.

The Deseret News in April published results of a poll it commissioned that asks what counts as cheating. One in four adults did not include a one-night stand on the list.