Not enjoying sex...

Hey all. So I am completely in love with my boyfriend. He truly is the best thing to happen to me..... but I never want to go through with sex. We’ve had it before and i never thought it was that great. And it’s not that I don’t want to, because I fantasize and think about it a lot and get horny, but as soon as we stop I just want to stop and i just want him to finish as soon as possible for it to be over. Idk what’s wrong with me?? Any tips?