Why am I acting this way? [dislike being intimate after some time]?

You probably need time to breathe from people every now any then. I am like that, when i get close to someone I want to break free and not talk to them... it is weird... I think it is because when you have a better relationship things get awkward and you know how to get to be good friends with someone, but you don't know what to do after that. Try and act as normal or read up on how to talk to people you know well. Social skills are where it's at.