Bf says he "misses" his ex?

My boyfriend, we've been dating for 5 months, has recently met up with his ex gf (he told me about this) to "put things behind them" and "be on good terms with each other". Well anyway, I was kind of wary about them hanging out like this, but I figured it would be better to just let him do it, rather than be a controlling b***** and say no. Well, I asked him how it went and he said it went well, they could be friends and there wasn't an "attraction" since the last time they saw each other(which I am presuming was before we started dating) but he misses her and thats all. I dont know why he would tell me that, because it makes me think that he is thinking about her all the time and that he would rather be with her if given the chance. Or maybe im just being paranoid. Anyway, should I talk to him about my concerns, am I being paranoid, or am I being stupid because he obviously still has a thing for his ex? Pleaseeeeee help me!