My father was a drinker. When I was younger I asked him why and he said it was his vice. After I got that response, I think I was 14 at the time, I stopped talking to him. He knew how much I and my brother hated it and how much it hurt our mother. Fastword time, he did end up quitting twice on his own. He did go back to it and is paying the price for it medically speaking, but he did try. Point being, no one forced him to and he had to want it for himself.
Be there for him if you can but if you don't have it in you, you are not obligated to save him so don't beat yourself up too much. It is an addiction but it is also a chemical process that happens in the body and regardless of how you view it or anyone else, his body tells him he needs it to live.