When you find yourself in a hole, usually, the best thing to do is to stop digging! I quit smoking at 40, stopping drinking now at 50... Tell your BF that if he stops now, it is infinitely easier than 3-5-10... years from now! The anger and problems your BF is "helping" by drinking, are very likely, being _caused_ by drinking. It's a pattern I have seen many times. You are still very young, if you have to, you can just move on. Stay strong, give an ultimatum and mean it. Good luck!
..Mike