" What I don't get is how someone I spoke to every day for almost 5 years can just so easily walk away and not want to talk to me at all? That really bothers me."
The reason is that there is something terribly wrong inside of him that you did not cause. In all likely hood it is from his childhood. Like a wounded animal he has gone off to heal himself. Let Go and let him. You didn't break him and can not FIX him.
