For anyone who has ever wondered what kind of psychopath stays friends with their ex, a new study has sought to uncover why people with "dark personality traits" (such as narcissism, duplicity, even psychopathy) maintain relationships after their expiration. For many people, staying friends with an ex is unthinkable. Even Psychology Today has urged the public not to befriend extinguished flames because: "they are less emotionally supportive, less helpful, less trusting, and less concerned about the other person's happiness."

In "Staying friends with an ex: Sex and dark personality traits predict motivations for post-relationship friendship," Oakland University researchers Justin Mogilski and Lisa Welling asked 860 subjects to list the motivations for their involvement with their exes. According to the Daily Mail, the researchers also surveyed the subjects to determine who had dark personality traits. "Previous studies have shown that people who score highly for these traits are more likely to pick friends for strategic reasons, and prefer short-term relationships," the Daily Mail reported. The researchers wanted to know if this were true for former lovers, too.

To determine this, subjects were tasked to rate their reasons for maintaining relationships with their exes by importance. The highest importance ratings were given by those who felt their former relationships were "reliable, trustworthy, and of sentimental value." But researchers also found that subjects who had "measures of dark personality" were more likely to maintain relationships with their exes for "practical and sexual reasons."

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In an interview with Broadly, the narcissism expert Dr. Tony Ferretti explained why people with dark personalities—particularly the narcissistic ones—would want cuddle with the cold corpse of their dead relationship. "Narcissists hate to fail or lose, so will do what they can to maintain some connection if they didn't make the choice to end it," Dr. Ferretti said. "They can experience narcissistic injury when rejected by a partner and have difficulties letting it go or healing from it."

Romantic relationships are important to psychological health, Dr. Ferretti explained, adding that intimate bonds boast many benefits: "People who are in close, healthy relationships are typically more physically active, more socially connected, live longer, and are physically healthier," he said, adding that partnered individuals are even less likely to smoke and tend to their overall health. "People who are in deep, close, healthy, and intimate relationships tend to be happier," Dr. Ferretti said. With such a broad list of benefits, it's no surprise that someone might want to keep a former partner close or to try to reclaim what they once shared together.

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But for narcissists, there are other benefits to relationships, Dr. Ferretti explained, and other motivations to cling to one that has ended. For example, a narcissist may feel as if their social status or position is amplified because of their partner. This is why some ego-maniacs acquire "trophy wives," Dr. Ferretti said, adding that in the mind of the narcissist, a trophy wife is an improvement to their self-worth and confidence. "Narcissists have a tremendous amount of pride and can't accept others being with their ex."