When I surveyed more than 1500 women for my book, Best Friends Forever: Surviving a Breakup with Your Best Friend, I discovered that most of them have an extraordinarily difficult time ending their friendships, even very toxic ones. It's not surprising. Like divorce, the potential losses can be staggering, extending well beyond the friendship per se.

That's because when two women are close, they tend to draw others into their circle: family members, neighbors, co-workers, and other friends. For example, if you're best friends with your neighbor, the chances are pretty good that your school-age children are friends, too. The kids may even be the raison d'être for the friendship. If you end your friendship, what repercussions will it have on them? Will they still feel comfortable having play dates? How will you feel when you see your ex-friend at a PTA meeting or on the soccer field?

If your friendship was centered in the workplace, there are also substantial risks of collateral damage. If you break off with a colleague, will you lose her support on work matters? Will you feel uncomfortable if you're assigned to work on the same project team or each time you pass her in the hall? Will other people around you, who knew how close you once were, feel awkward or ask questions? Might she say something that would irreparably impugn your reputation? If your ex-friend is in a supervisory role, could it pose a threat to your employment?