After I asked him to stop talking about me behind my back the first time, I don't think he ever promised to stop. I think he just assumed that he knew it didn't matter regardless of how uncomfortable it made me, and he kept on doing it. He's extremely arrogant- he will never accept that other people know more than him in certain areas, and he reacts angrily if you try to tell suggest that he might be wrong. Combine that with an overall cluelessness about mental illness and he's bound to do some destructive things.

How do I show him that he needs to stop? He's extremely stubborn and is now angry with me for objecting to him talking about me again. He says that he's going to keep doing it and that I need to get over it. I can't get over it and since it's my mental illness, not his, I don't think I need to. I feel like a mental health professional could tell him in plain terms that he should stop and he wouldn't listen.