Just wanted to point out that if someone is attracted to you then, by definition, they're not out of your league.
Ditto! Don't sell yourself short or make yourself feel like you're somehow inferior to him just because he models. You clearly ARE in his league, otherwise he wouldn't have hooked up with you multiple times.
Was he possibly already in the relationship before you starting hooking up? That could certainly be why he wasn't looking for a relationship with you.
Until you communicate, there is no way you can know what the real situation is. Maybe his bf is fine with him hooking up, and maybe not. Asking him about it in a way that is non-confrontational and not charged is the best way to proceed in my opinion. You have every right to know what kind of situation you are in. If you find that you are not able to ask in a way that is not confrontational, then it sounds like there is more at stake for you than you may be willing to admit to yourself and maybe you're wishing that you were the bf and not the hookup? Maybe not, I have no idea -- only you do.
The bottom line is that people react to the kind of energy that is presented to them. If you "confront" him as you put it with that type of energy, he is going to react in a confrontational kind of way. If you ask in a way that is not charged or accusatory, he's likely to just be open about his situation, bringing you into the loop.
Once you have all the facts, it will be much easier to decide what you really want.