How should I handle this?

My boyfriend (of 1 year) went out this weekend, diving, with his old girlfriend. I don’t know much about their relationship, except that they were together for a few years and he will never say anything bad about her. A few months ago, while we were visiting his parents, he made me stay home while he went to “have coffee” with this same old girlfriend, for a couple hours. He was going through old stuff in his room and kept all the love letters that she had sent him. He claims they are still very good friends. I’ve seen that he texts her and messages her on Facebook all the time. I am not comfortable with this AT ALL – I just don’t understand how you can be friends with someone that you were once in love with (how does that not bring up old feelings). I’m really hurt that he’s doing this. Plus, I am 95% certain she doesn’t even know about me – he keeps his relationship status hidden on Facebook.

Am I in the wrong here? Am I overreacting? I am a very insecure person, I’ve been cheated on by previous boyfriends and I don’t want to be put through that kind of pain again. How should I handle this? I really don’t want to end the relationship, but then again, I don’t think I can handle him being tied up with his ex-girlfriend.

Help :(