I am so sorry you are going through all of this. It is time to find yourself again and develop a life that makes YOU happy. He is an adult, and needs to live with the consequences of his choices like the rest of the adults in the world.
Please attend alanon meetings and contact NAMI to see if they have any family groups or classes in your area. These will help you detach and learn to cope in new ways. If you do this for no other reason, know that if the family goes to alanon, the alcoholic/addict has a 30% better chance of getting and staying clean/sober. I know that if your son was in school and you could spend 1 hour a week or so going to meetings to raise his grade from a 60% to a 90%, you would have done it happily. Most moms would. This is so much more important than a high school grade, and is harder, but it is worth it. I know because I have been to alanon to learn to deal with the alcoholics in my family. I am what is knows as an adult grandchild of an alcoholic as well as the sister of one. When I first got married, I had HUGE issues with my husband's very casual drinking. I went to meetings when I realized my reactions and fears were FAR from normal. My family was NOT happy when I applied what I learned to my brother, but it was another 12 years before my brother hit bottom and the rest of the family realized he really did have a problem.
You seem ready to change things. Your son has huge problems, but they are NOT NOT NOT your fault. You did the best you could. You never woke up one day and asked yourself "How can I best ruin my child's life today?", so it is NOT your fault that he has problems. He is now an adult and whatever happens in his life is due to him, period. You deserve a life free of conflama (conflict + drama = conflama) and full of things that make YOU happy.