Mersault22, I completely understand the overwhelming sense of obligation and the feeling of being sucked into a drama that isn't your own but out of which you don't see any escape.
What I can tell you is that if your brother has no children, I may be easier to set boundaries or rules or whatever limits you see fit so you don't lose yourself and your mind in the process of helping him.
Like you, I buried my grandparents, my alcholic father and recently my alcoholic sister. But like you I have a family: two sons, a loving partner, and things to look forward to in life.
Hugs to you, it's hard to watch someone we love struggling with that level of addiction. In my experience, the hardest thing was that I reached a point that I hurt so bad too I couldn't help at all.
B.