Mutual friends are plentiful while you are in a romantic relationship—a recent study shows 63% of married couples met through just such a network. But what happens to them if the two of you call it quits? Suddenly these same friends you once called for coffee and double dates could be called on by your ex to trash-talk you.

"My ex and I didn't talk about how we were going to divvy it up, but I think it was important that neither of us made our friends choose," says Melissa, 23, about a messy breakup. "I know that he badmouthed me the summer after we broke up, which made one or two of our mutual friends shun me. But I actually did have some of our mutual friends say to me, 'we love you, but is it okay if we are still friends with Mike, too?'"

After the initial pain of the break up subsides, many couples wonder if it's possible to "share" mutual friends with an ex. But is joint ownership a sound strategy? The answer: It depends.

"The cause of the breakup is very important," says Catherine Sanderson, PhD, an associate professor of psychology at Amherst College who researches close relationships. "Infidelity is more difficult for people to cope with than, say, a mutual breakup. If the couple started as friends with similar interests and one had to move for business, they are more likely to be acquaintances and maintain mutual friendship after the separation."

And it all depends on who you're trying to stay friends with. "The mutual friends that are most influenced are newer friends, 'couple' friends, because they are asked to choose sides," says Sanderson. Mary, 47, experienced this firsthand when she and her husband divorced.

After learning that he was having an affair with a mutual friend and coworker, "It was a really bad situation, so I was focused on starting over," she says. "I found that my friends from before the divorce were still mine afterward. My large family was also a primary support. Honestly, due to the circumstances, I really didn't really want anything to do with my ex or any of our coworkers." Luckily, Mary mentioned that she was able to cut all ties to them.

And sometimes that's okay. In the throes of heartbreak, what you need are a few go-to friends, not a Facebook-sized army of acquaintances. "At this point in time, a big friendship network isn't necessary," says Sanderson, "but what is are the subset of people who are in your corner.

These are the people whose loyalty you're sure of and who you don't have to worry will report back to your ex." In some cases, says Sanderson, they may almost act as your representatives, making sure rumors are nipped in the bud.

Still need ways to mend a broken social circle? Try these tips:

• Tell your side of the story. Nobody likes a martyr, but if it was a messy separation, make sure friends in common know your side. "The person who goes 'public' with this news first is probably better off, since the way they frame and describe the situation are important," says Sanderson.

• Act with integrity. Whatever the situation, both parties are ultimately hurting. And while it is okay to vent a bit, don't trash-talk your ex in front of mutual friends. Not only is it bad dating karma, but it also makes for an even more uncomfortable situation.