What should I do?

Does anyone else really want sex, but then when it starts happening you become uninterested and no longer feel like having sex? My boyfriend is good at sex, but I always fake it when we're having sex to make him feel better. I do orgasm, but I just get upset afterwards. I know he would be upset if he found out, but I have an obsessive need to please others. We've tried other positions, but it doesn't seem to matter. I've been raped a few years ago so he's the only one I've consented to. What should I do?