Should I forbid my LTR to chat and speak with her ex boyfriend?

I don't understand what can be a proper response here. On the one hand, it seems to me that I'm not self-confident enough and am afraid of competition by raising the topic. On the other hand, I don't quite like the fact that she continue to communicate with him.

A lot of things from TRP were a surprise for me and were quite counter-intuitive so I want to ask you guys what is your opinion and experience with the topic.