It seems you placed boundaries in the first place, but still allowed him to communicate with her. However, they sure are talking a lot for being broken up. It's perfectly normal for you to be uncomfortable about the fact that he is talking to an ex regularly, in my opinion you are not being over possessive. Chatting on Facebook occasionally is one thing, but unless you are heavily exaggerating in your post, I would not describe your behavior as possessive. In fact, you being able to identify your behavior as potentially possessive shows that you have an adequate level of self awareness.