Engaged-to-be-married individuals tend to have the most negative attitudes about best friends of the opposite sex, according to new research published in the Journal of Relationships Research.

“My co-author and I both study interpersonal communication, and this subject was part of our collective research agenda. Previous research had examined jealousy among cross-sex friends in general, but not among best friends,” said study author Eletra Gilchrist-Petty an associate professor at the University of Alabama in Huntsville.

“There is generally a much more intimate connection between a male and female who consider themselves best friends. On a personal note, I have a really good cross-sex friend, and while my husband has never exhibited any jealousy regarding our relationship, I have friends and other cohorts who have had personal experiences with jealousy in a cross-sex best friend situation.”

“So I really wanted to do this study to examine how jealousy is experienced and expressed when one has a romantic partner who considers someone of the opposite sex his or her best friend,” Gilchrist-Petty said.

For their study, the researchers surveyed 92 men and 254 women who had a current or former partner with an opposite-sex best friend. The participants ranged in age from 18 to 64 years.

Single individuals were the most likely to agree with positive statements about opposite-sex best friends, such as “I would not mind having an opposite-sex best friend,” “Men and women can be best friends” and “I would date someone that had an opposite-sex best friend” — followed by dating individuals and married individuals.

Engaged-to-be-married couples, on the other hand, tended to have the most negative feelings about cross-sex best friends.

“Of all the relationship types, we found it quite interesting that engaged-to-be-married individuals had the least favorable attitudes regarding cross-sex best friends,” Gilchrist-Petty told PsyPost.

“As we attempted to make sense of this finding, we theorized that perhaps engaged couples feel that they are almost there — meaning almost married. Hence, they are especially protective of the relationship and do not want anything or anyone, including a cross-sex best friend, to potentially jeopardize their upcoming marriage.”

“Also, planning a wedding can be a very stressful event, and it is logical to assume that maybe the engaged individuals are guarded when to comes to their fiancé having a cross-sex best friend because the potential threat of that individual can escalate the stress and anxiety the engaged couple is already experiencing as they prepare for an upcoming wedding and the merging of lives,” Gilchrist-Petty explained.

The researchers also found evidence that jealousy influenced how people behaved towards partners with an opposite-sex best friend.

Those who agreed with statements such as “It is not acceptable for me if my partner sees many people of the opposite sex on a friendly basis” were more likely to report engaging in mate protection strategies aimed at communicating about and derogating the potential romantic rival.

“In other words, when a relational partner perceives that a cross-sex best friend is a potential threat to the romantic relationship, he/she experiences preventive jealousy and is therefore motivated to minimise the potential threat by using communication that conveys possession and degrades and/or restricts access to the cross-sex best friend,” the researchers explained.

But the study — like all research — includes some limitations. The study focused solely on heterosexual relationships, so it is unclear how well the results generalize to non-heterosexual relationship.

“We did not control for any personality/social traits that could potentially predict whether or not a dating partner might have negative attitudes about his/her partner’s cross-sex best friend,” Gilchrist-Petty added. “For instance, previous research has correlated jealousy to several personality/social traits, including low self-esteem, neuroticism, and anxious attachment styles. So a great follow-up to our research would be an exploration of how certain traits compound the jealousy and negative attitudes regarding cross-sex best friends.”

Whether heterosexual men and women can be best friends — and stay “just friends” — is still hotly debated.

“I think if we really consider where some of our ideas come from regarding men and women as friends, we cannot deny the influence of pop culture and media representations. In the latter 1980s, the movie ‘When Harry Met Sally’ asked a profound question, ‘Can men and women just be friends?’ Of course the film implicated ‘no’ when the two main characters became romantically involved,” Gilchrist-Petty said.

“Nonetheless, some 30 years later we still see this relationship dynamic played out in pop culture, where a multitude of heterosexual men and women start out as just friends, but then it morphs into something romantic. These constant media representations inform our real-life assumptions that at least the possibility exists for our romantic partner to become intimately involved with his/her cross-sex friend,” she continued.

“So, there is no easy answer to the question, ‘can men and women just be friends.’ Perhaps the best answer is, yes, but it’s complicated, especially if the cross-sex friends are in committed relationships.”

The study, “Cross-Sex Best Friendships and the Experience and Expression of Jealousy within Romantic Relationships“, was authored by Eletra Gilchrist-Petty and Lance Kyle Bennett.