It seems to me that he has a great fear of letting people in, and getting emotionally close to others. If I were to guess, I would wager that your friend is probably scared of being abandoned, and possibly lashing out at people to lessen his dread of such an event. I would suggest you talk to him as openly as you can about the issue. Do it in a non-confrontational manner, avoiding any accusations of his antisocial behavior. Instead, directly address the insulting way he treats you, how it makes you feel. It wouldn't be a good idea to bookend these suggestions with a threat that you will sever contact if he doesn't, as that will likely trigger a panic response which could be ugly. If, after you've tried to ask him to face his issues, he is clearly making no attempt to try to struggle with his behavior, then ending things might be your only option.