I have no reservations when I have casual sex. However when one of these flings turns into a relationship and things get serious I don't want to have sex with them anymore. It has happened with my last three boyfriends and has been the primary reason for my breakups. It feels like a normal relationship...we are best friends, we do almost everything together, I care about him tremendously, but I get scared when he wants to have sex. Why can I only have emotionally detached sex?