You seem like a person that has a big heart that just wants to help someone you care about. But the truth is you can’t help him. It’s is completely out of your control and your ability. He needs professional help and only he can decide when he will get it.
I think the reason he is being mean to you is simply to lash out at you for not wanting to continue a relationship with him because it scars his ego. It’s is probably best not to continue any type of friendship or relationship with him until you know for sure he is getting the help he needs and is willing to accept calmly that you and him won’t continue to have a romantic relationship.