As the divorce rate in the United States remains at 50 percent, many couples are becoming extra cautious in choosing the right partner to marry. According to the calculations of Philip Cohen, sociologist from the University of Maryland, the marriage rate has fallen from 90 marriages a year per 1,000 unmarried women to just 31 marriages — a 66 percent decline. The data suggests that if the marriage rate continues to steadily decline, by the year 2040, there will be no women who are getting married. However, 75 percent of women in the United States are found to be living with a partner without being married by age 30, an increasing trend that supports cohabitation as the beginning of family life. The decline of the marriage rate in the U.S. and the increase in cohabitation in unmarried couples have prompted researchers to examine sexual faithfulness and the characteristics of partners who have extradyadic sex — sexual relations outside their serious romantic relationships.

In a study published in the Journal of Sex Research, Amanda Shaw, lead author of the study, and her team of researchers examined how many people who are seriously involved in romantic relationships have sex with someone else and the characteristics of such individuals. A total of 933 unmarried couples — between the ages of 18 and 35 and involved in serious romantic relationships that have lasted at least two months — were part of the study. On average, unmarried couples already hit the two-year dating mark in their relationships, which they reported to be important and ongoing.

During the start of the study, the participants were asked about several personal characteristics including age, education, and number of sexual partners. The unmarried couples were also asked about their relationship characteristics including relationship satisfaction and frequency of sex. Researchers followed-up with these couples 20 months later to evaluate whether or not they had extradyadic sex.

The observation of individual and relationship characteristics was used to determine who was more likely to have sex with someone other than their partner during the 20-month time frame. The results of the study showed that 14 percent of unmarried couples had extradyadic sex since they began participating in the long-term study. Those couples who already sex with someone else while in a romantic serious relationship were excluded from the analysis of the study to accurately predict what leads unmarried couples to have extradyadic sex.

Cheating Predictors: Relationship Factors

Relationship quality was found to be a strong predictor of which individuals in unmarried romantic relationships were most likely to cheat on their partners. The following relationship factors were helpful in predicting:

· Lower relationship satisfaction

· Lower levels of dedication (commitment) to the partner

· Higher levels of negative communication

· A history of physical aggression in the relationship

· Not having mutual plans for marriage

· Suspicion of partner having sex with others

· Partner has had sex with another

Cheating Predictors: Individual Factors

While individual factors were found to play a lesser role in determining what may lead an unmarried couple to cheat, the researchers found these common characteristics among the partners who did cheat:

· Having more sexual partners prior to the present relationship

· Greater use of alcohol

· Having parents who never married

These relationship and individual variables were found to be the strongest predictors of cheating in a unmarried relationship. "Overall it was the characteristics of the relationship that mattered most—things like commitment, communication, and satisfaction,” said Galena Rhoades, Ph.D., study co-author and a research associate professor at the University of Denver, to Women’s Health.