Arg...hard to explain!! Please help..?

Been with my bf quite a few years and ive completely gone off of him. I dont find him attractive, i'll have sex with him because im horny but I don't feel close to him at all. He always wants to know where I am and what I'm doing. He doesn't seem to believe me when I tell him and I feel like im treading on eggshells when I see him. He is very insecure because I have been getting really fit and toned and he feels like I am going to leave him. IT DRIVES ME CRAZY! I don't want to be around him at all. Been together like 6yrs so its hard to just dump him over this but if it carries on, I dont know how much more I can take! I've spoken to him about it many times and he says that I am pushing him away because I am so distant and he is worried. I say I am so distant because I can't relax around you and be myself without upsetting you or you thinking im lying. Its like a circle and I don't know what to do..any tips?