Yes, you can be friends with an ex. Whether or not that's a good idea depends on your personality, your ex's personality, the nature of your relationship, and a host of other factors.For many people, the idea of staying friends is untenable. After all, that's why breaking up is called "ending a relationship." In most cases, the relationship...ends.Scientists have looked into post-breakup friendships, and some of the research has interesting implications for these types of relationships. In one such study, researchers identified four common reasons behind the behavior: security, practicality, civility, and unresolved romantic desires.Unsurprisingly, participants in this last group had more negative outcomes-their friendships ended, or they were unhappy in their other relationships. People who stayed friends for security or for practical reasons had more positive outcomes overall, but people who stayed friends for practical or civil reasons were less likely to stay friends in the long term.In other words, if you're looking for a long-term friendship, you should want the security of the friendship; other factors shouldn't come into play. For instance, if you want to maintain the friendship because you're worried that your mutual friends will choose a side, your friendship with your ex probably won't last very long, even if you are able to sustain it for a short time. More importantly, if you have romantic feelings for your partner, don't expect them to disappear simply because you've changed your relationship status on social media.There are other reasons to consider a clean break. Another study on post-breakup friendships yielded a surprising result: Men who maintained these relationships were more likely to have "dark personality traits" associated with Narcissism and sociopathy. Men were also more likely to rate sexual access and pragmatism as important reasons for continuing the friendship.Still, "your ex might be a psychopath" isn't a great reason to cut off contact entirely. Plenty of people are able to maintain worthwhile friendships with ex-partners, so there's no hard-and-fast rule.If you're considering a friendship with an ex, ask yourself why you want to keep part of your relationship intact. Be honest with yourself-if you've got any unresolved feelings whatsoever, it's probably a good idea to cut ties, at least temporarily, until you're both comfortable with other romantic pursuits.If, however, you feel that your relationship is better as a friendship (and if you're sure that your ex feels the same way), go for it. Good friends are hard to find.