Paul Bradbury / Getty

In 1989, When Harry Met Sally posed a question that other pop-cultural entities have been trying to answer ever since: Can straight men and women really be close friends without their partnership turning into something else? (According to The Office, no. According to Lost in Translation, yes. According to Friends … well, sometimes no and sometimes yes.) Screenwriters have been preoccupied with this question for a long time, and according to a new study published in the Journal of Relationships Research, the question is also likely to be on the minds of people whose romantic partners have best friends of the opposite sex.

For the study, Eletra Gilchrist-Petty, an associate professor of communication arts at the University of Alabama in Huntsville, and Lance Kyle Bennett, a doctoral-degree student at the University of Iowa, recruited 346 people, ranging in age from 18 to 64, who were or had been in a heterosexual relationship with someone who had a different-sex best friend. When they surveyed participants’ attitudes toward cross-sex best friendships, they found that people who are engaged to be married look more negatively on those friendships than married, single, or dating people. They also found that people who are skeptical of cross-sex best friendships in general are more likely to “lash out” at their partner when they feel threatened by the partner’s best friend—as opposed to constructively communicating with their partner, or with the friend, about the situation.

The possibility of romance between friends of the opposite sex has not just fascinated writers and directors for decades; it has also been a frequent topic of study for psychologists and sociologists. (According to prior studies, sexual attraction between cross-sex friends tends to decrease the overall quality of the friendship—and is also extremely common.) True platonic friendships between men and women of compatible sexualities have, of course, been common for what researchers believe to be a few generations now. But movies that depict platonic friendships evolving into something more—like When Harry Met Sally, as well as My Best Friend’s Wedding, Friends With Benefits, Zack and Miri Make a Porno, and Drinking Buddies—seem to insist that there’s always the potential for a male and female pair of best buddies to act on a latent attraction to each other.

Pop-culture narratives like these tend to reinforce the idea that the boyfriends or girlfriends of people with a different-sex best friend should always be on their guard, too—which is perhaps why, as Gilchrist-Petty wrote to me in an email, she and Bennett found most of the participants in the study to be surprisingly lukewarm on cross-sex best friendship as a concept.

“Heteronormative assumptions have historically socialized us to consider men and women as romantic or sexual partners,” she wrote. “Hence, individuals tend to have at least an understated assumption that the friendship between men and women can evolve into something more than a benign friendship. This assumption appears to be pretty widespread.”

Alexandra Solomon, an assistant psychology professor at Northwestern University and the instructor of the university’s Marriage 101 course, who was not affiliated with Gilchrist-Petty and Bennett’s study, wonders whether the correlation between negative attitudes toward opposite-sex friendships and negative or violent expressions of jealousy could be due to participants’ personal beliefs about gender roles.

“It speaks to a bit of a rigid, dichotomous way of thinking—I suspect there’s a layer in there about how much [the subjects] endorse traditional gender roles,” Solomon told me. A woman with more traditional ideas about gender might feel threatened by her boyfriend’s female best friend because, as Solomon put it, “she may have this idea that I ought to be your one and only, and I ought to be able to meet all your needs. If you love me, then you’ll only turn to me.” A man with similarly rigid or traditional ideas about gender roles, she added, might feel territorial or possessive, as though his female partner belongs to him and only him. (Gilchrist-Petty and Bennett did not control for or take into account individual participants’ personality traits or belief systems.)

The study results also suggest that relationship status can play a role in people’s level of trust in cross-sex best friendships. Gilchrist-Petty wrote to me in an email that of all their findings, she was most surprised that engaged couples were the most skeptical. Engaged couples may be particularly protective of their relationships because they’re almost across the matrimonial finish line, she posited, “and do not want anything or anyone, including a cross-sex best friend, to potentially jeopardize their upcoming marriage.” In the study, she and Bennett also note that engaged couples are in a uniquely stressful situation compared with single, dating, and married people: Not only are they transitioning to become assumed life partners, they wrote in the study, “but they are often dealing with … merging lives and planning a wedding.” As they note in the study, this can include family problems as well as financial constraints, both of which are known to place long-term stress on people and relationships.

Stress can certainly be a risk factor for feelings of jealousy, Solomon noted. “When any of us are under stress, we do kind of regress a bit, and fall back on less healthy ways of coping. Insecurity can spike, and if you’re not particularly comfortable in your own skin, you’re more likely to want to control the world around you,” she told me. “I think staring down this really big identity shift—a relationship-status shift, a life-commitment shift—just awakens insecurity that we don’t always know how best to cope with. So to get controlling of a partner would would just seem like a way of coping.” An unhealthy way of coping, to be sure, she added, “but it’s understandable.”

Solomon also lauded the study’s efforts to consider feelings of jealousy and expressions of jealousy separately. They’re often conflated, she told me—for example, the concept of a “jealous lover” is commonly invoked to describe both lovers who feel jealousy and lovers who exhibit controlling behaviors toward their partners. To consider the feeling of jealousy as something that may not necessarily have a corresponding action, she said, can help destigmatize it and clarify why people might be particularly vulnerable to it.

“Maybe this is another reason why engaged couples struggle the most,” she added. “When we fall in love and make a commitment to someone, we become actually, neurophysiologically tied to them. Our intimate partners live in our bones; they matter so much that they co-regulate each other’s physiology. So of course, [anything that gives] the sense of, Oh my God, I’m gonna lose you, is really threatening and terrifying. But that’s separate and apart from what you do with that.” In other words, she said, there’s a strong distinction to be made between I love you, and I’m reckoning with how much I need you and I love you, so I have to control you because I’m so afraid of losing you.

“We tend to very quickly go from the experience of jealousy to acting on it,” Solomon said. But if people instead consider the feeling of jealousy as an opportunity to reflect on their own emotional state and what might be affecting it, it can be fruitful and enlightening. In other words, Solomon noted, Gilchrist-Petty and Bennett’s study suggests that nothing is inherently wrong with privately feeling jealousy toward a partner’s best friend of a different sex—but that there are healthy and unhealthy ways to act on it.

We want to hear what you think about this article. Submit a letter to the editor or write to letters@theatlantic.com.