So here's the thing. Say you tell him about your past in an effort to try to get him to understand, and it turns out he can't deal with it, and you wind up alone. Ok, well, that sucks. But imagine you don't tell him about your past, and instead you act passive-aggressive and insecure. Well, over time you'll drive him away and you'll wind up, you know. Alone. So the worst case scenario in opening up is the same as the best case scenario in carrying on the way you are. Really you've got nothing to lose, and if he rejects you after you attempt to share or if he can't work with you then he isn't the right fit for you in the first place.

Good luck