Gerda - let's assume for a moment that his mind IS unraveling, that he has prefrontal dementia or some such. (Although I suspect he was always a jerk and you just saw what you hoped to see in him - I know, I'm guilty of that too, my ex's narcissism didn't really become clear to me until after he left although in retrospect it was always there.) He is not severe enough for you to get a court order to give you control over him. His family doesn't acknowledge his mental decline. And he is refusing to hear you or get any help.
At this point your job is DONE. You cannot control every thing that happens to the other person. I couldn't stop my ex from divorcing me even though I knew his two concussions in 3 weeks just prior to his asking had something to do with it. Sometimes we simply cannot save them from themselves. (And sometimes this is who they really were all along - even with the concussions, I have to admit that my ex's issues weren't caused by the concussions, only slightly worsened by them.)
Accept that you cannot save him and let go so that you can save YOURSELF and your children.
