Originally Posted by
alcoholicBF 
I can't give an ultimatum like "its me or the alcohol" because I know in my heart that wouldn't really be a choice for him.
What wouldn't be a choice? Would he choose alcohol?
I've heard several people wishing that their wife/girlfriend/someone had given them that choice. I myself too. I also heard people being thankful that they were given it. If he continues drinking he will destroy 2 lives. I absolutely think it can be the best thing to do.
But before that, I would confront him while he is sober, you and his brother together.