So Called Friends

Why do the people that you are supposed to be able to trust always let you down.... For instance I had a friend that I really cared about but the minute I turned my back she was telling my ex things that I was doing and saying like I was doing something wrong... I wasn't with him so it really didn't matter what I was doing but I guess that she thought that he should know things anyway.... It wasn't the fact that he knew things. It was the fact that she was supposed to be my friend and not go around talking about me.. I guess in the end you always find out who your true friends are and that is sad that people are so bored with their lives that they have to go around and talk about other people. If you have any advice on what I should do then send a comment and let me know...