How do I bring this up with my boyfriend without sounding jealous and controlling?

I just have this nagging feeling that my boyfriend is still in love with his ex. I don’t know much about their relationship, but I think they were sort of “high school sweethearts” – she ended up leaving him for some other guy (whom she is still with). I don’t think my boyfriend has moved on. They are still really close friends. He took me back to his hometown today, and then he left me to go see her. She’s leaving town for a few months and he seems really upset by it. They text all the time, etc. I know he’s not cheating on me. I know she is over him, but I don’t think he is. And it bothers me, I don’t know why – It just makes me feel not good enough. And that if he could, he’d pick her over me. I feel like I want to bring this up with him (If I could get him to stop talking to his ex completely I’d be a happy girl LOL but I know that won’t happen and I wouldn’t ask that) I don’t even know what I want to see happen. But I’m afraid to bring it up to him because I don’t want to be the jealous, controlling bitch of a girlfriend, you know? Help!