SWC your statement "I won't give up but I feel like waving a white flag". (sorry don't know how to but it in the little yellow box)
You don't have to "give up", think of it as a relay race. You and your son are in this race (for a healthy life), You start the race when he is born, but now YOU NEED to hand off the baton TO HIM, HE needs to finish this race, YOU are on the sidelines cheering him on, but it is up to him.
My difficult child has a different addiction,he was put on probation. He was doing well had gotten his own job, was living with a grandparent and helping them with yardwork and such, and he was was certain to be at his group and therapy classes, But he broke his probation; went off his medications, etc., he was due to have a polygraph and realized he would never pass so he told his PO, and he landed in jail. I refused to bail him out, as I had the first time. His friends bailed him out then he and them were staying with grandparent and that is not right so I kickrd him out. OMG that is one of the hardest things I've done, but I have seen him slipping, I've confronted him on him not taking his medications but he always had a shpeal about it. It hurts like hell, but I also have my daughter to think about. My husband unfortunately will not discuss any of this, his reaction was against me, saying I would walk all over anyone to protect difficult child, if I was willing to do that then why didn't I bail him out? So right now husband and I don't have much to say to each other. husband has gone off his medications also, yipee, I am tired of being the glue.
You need to focus on your daughter and her joyous day, the problems with difficult child will always be there. But your daughter has one SPECIAL wedding day, and difficult child needs to realize he is not the only one.
Love your screen name, take it into action.