I asked my boyfriend (out of interest) who he'd go out with if he didn't go out with me....?

I'm thinking that you should have never brought this up as some things are better left unsaid. Overall, I think you should tell your boyfriend the situation and how you feel about it (honesty is the best policy) and see how he reacts. If he really loves you, then he'll lovingly reure you that you are the only one for him but if he doesn't answer or just trails off, then I would break it off with him before he can hurt you.