It’s the question that will haunt us until the day we die: Should we stay friends with an ex? It’s not an easy feat to accomplish, but it can be done. Recent research has given us a warning on the matter, though. If your ex is trying to keep a friendship with you after you’ve broken up, there could be something more serious going on. Turns out, they might be a psychopath or a narcissist. Let us explain.A study published in Personality & Individual Differences surveyed a group of people about why they stayed friends with their exes, then asked another group of folks to rank the importance of these reasons. In the meantime, they also conducted tests on the participants that measured “dark personality traits”. Sounds ominous, doesn’t it? It kinda is.The verdict is pretty simple: Psychopaths and narcissists are most likely to request friendship after the romantic relationships has come to a close. An author of the study said, “Individuals who score higher on measures of dark personality tend to choose friends for strategic purposes. Thus, it is likely that these traits will be associated with valuing friendships for utilitarian or instrumental reasons, such as to maintain sexual access.”According to the results, the most popular reasons people stayed chummy with an ex was for sentimental reasons. Men were much more likely than women to name the possibility of sex as a reason to be friends. But it was the psychopaths who cited “sex and practicality” as the top reasons for keeping a friendly relationship, as they’re the ones who tend to use people to gain things for themselves, no matter what stage of a relationship they’re in. Yuck.Of course, this isn’t a hard, fast rule for all the exes in your life who have wanted to maintain a friendship. But think twice if you’ve got an ex in particular who just can’t seem to cut off communication, because there might be an ulterior motive that points to psychopathic tendencies.