I'm sorry you are going through this with your BIL, but it truly is beyond your control. When he has had enough, he will make the choice to work with professionals to change. Unfortunately, from your post it appears his addiction has resulted in your panic, fear, worry, need to take on the burden, etc. that is so much a part of this family disease.
I too urge you to read all you can about addiction and codependency and to try some Alanon or Naranon meetings. Try 6 and see if that's the place for you. I knew when the rooms helped me to get some tools to address my part of this family disease, and when I felt the love and support of people who had been where I was, that Naranon was the place for me. Sending positive thoughts and prayers.