This man needs psychiatric help. He will not get any better without it. Since he is an adult, he must go there and get help himself. If he refuses to do so, and I bet he will because he sounds like he has very serious antisocial/ narcissistic issues, then you can only try to have his committed against his will if you believe he is a danger to himself or to others, and then they will only keep him if they agree with you.
I think all you can do for him now is to urge him to get psychiatric help --- because you love him and don't want any more bad things to happen to him. I think praying for him is a good idea too.
But he is an adult-- he has to fix this himself now.
you used the term that came to mind for me - sadistic. he needs jesus. the boy is a downward spiral and im sorry to cut you the bad news but what you couldnt do as far as correcting him in childhood, you sure cant do now. forget it and if you havent started already, pray for the man