I guess you have to be honest with yourself and ask this question "What are you getting out of this?"
He is 34 for goodness sake, has an addiction that only he can work on or fix.
My son has drug and alcohol problems too. He is 24. I dont feel sorry for him anymore, because he knows there is alot of help out there and its up to him to live his life. As much as I hate seeing him like this, it is his choice and I had to accept it.
Why should your other children have to put up with this, and understand it. Victims like your son love the attention, why not give some back to your other children and grandchildren.
Look at it this way, you fear his death. I did too....... He isnt going to do anything like that why he has his mother bending over backwards for him, is he? Sorry, but if you went to birthday parties, and lived your life, and loved your other family members, he may take a little notice and start growing up.
It seems you have an answer for all his problems, but unfortunately you are giving him reasons to keep on doing what he has always done. Get out of his life and start living yours.
I know you love him, care and fear the worst but he knows that, and you need to start putting all that energy into your life and your other children. Right Now.