Bad friends are best avoided completely, and you should be wary when you meet new people. Always make sure that you clearly understand the motivation of the other person before you form a bond of close friendship. Some people will try to make friends with you because they covet what you have. Others may seem nice but they may not be capable of true loyalty or legitimate closeness. A bad friend can cause devastation on a scale that even your enemies may not manage, because they are closer and know more of your secrets.
Things change. And friends leave. Life doesn't stop for anybody.
Don't tell me what they said about me, tell me why they were so comfortable to say it around you.