My friend, he is already doing the things you are scared he is going to do. The only thing you can control is what you do with that information. You cannot change him, so if you want change, you must change YOU.
Feeling sorry for someone is not a reason to stay. You can care for someone without placing yourself in the line of fire, or sacrificing yourself to make them more comfortable. Sendng you strength and courage to accept him for who he is right now, and to make your plans accordingly.