I have no real advice Doodle
I decided a while ago, for my own good, that my parents were gonna do what they were gonna do, and it was best for me to do or say what I could...and then leave it.
That's not cold hearted IMO - I struggled with it, but I see it now as admitting that some things are beyond my control...and that's going to happen sometimes.
I agree with the others - let him know you care and you're concerned, let him know you're there to help if he decides he needs it...certainly pray...but try and not let someone else's mistakes eat you up.
D