Unfortunately for you, your boyfriend is using you like a prize to get back at the ex.
If you were that important to your boyfriend, he wouldn’t be using you at all. He clearly isn’t over is ex and that’s a problem. He may not love her, but if he hates her with such a burning passion, that’s almost as bad, because he’s always thinking of her.
You probably are a great catch, unfortuntely he’s not treating you like a great catch, he’s treating you like a pawn in a nasty little chess game.
It would be totally different if you just happened to bump into her, which you probably would, eventually, and he just introduced you as his girlfriend and was very polite and calm about the whole thing. Especially if after the event, he said to you, “Frockdialect, I’m so glad you came into my life. Thank you for making me see how things can be really great when you’re with the right person.” and then he would make no mention of the ex girlfriend. That would be classy. What he’s doing ain’t classy.
You might want to say something like this to him, “Fred, you know I love you and I think that you love me too. I know it was hard when Alison broke up with you, but we’re together now and I hope that you can get over her and stop thinking about her, and just move on with our own relationship. I’m glad that you think you got a better deal with me, at least I hope that’s what you think, but I really don’t want to be shoved in Alison’s face as some sort of prize. I just want us to move on together, and put her in the past. Can you do that for me?”
Then pay attention to what he says. If he agrees with you, it’s all good. If he gets a little pissy and tries to tell you that’s not what he’s doing, be a little wary of his intentions. Good luck with this situation : )