I'm sorry for your situation, i don't know why someone would do that to another person, is he mentally ill in any sense, maybe he needs help, and is looking and it is a cry for help because of the way he treats you. About your friends, they will see what is going on, most likely, or you could talk to them and explain what's going on. They probably already see it if he's talking behind your back. You must feel lonely dealing with this, so please talk to a friend.