They are right, If he doesn't want to stop then you can't make him.
Just be there for him to chat to if he wants. Spend time with him and show him that he can still enjoy life (cinema, bowling, having a laugh etc). All of this will help him and enable you to try to help him reduce the frequency with which he cuts.
Is he receiving any help professionally?
~ The journey of a thousand miles begins with a single step ~
* Nothing in the world has ever been accomplished without passion *