Dear Panda,
Isn't it sad that after 4 1/2 years, he didn't have much of a reaction to your ending the relationship? I suppose it's because his addiction is more important than anything, including you. I know that sounds harsh, but it's true.
I have been dealing with my son's addiction for 5 years. I recently joined this forum and started going to Al-Anon because I finally got it through my head that I cannot fix him, and that even as close as we are (or used to be), his addiction is his priority. I have now decided to have No Contact with him, and that has been going on for almost a month. It was incredibly hard at first, but it's getting better. I feel that I am reclaiming my life.
I have also been in a relationship with an alcoholic, though thankfully it wasn't for that long. He was a fantastic guy, and when he wasn't drinking we were fantastic together. However, he has demons that he is dealing with that are deep-seated, and he drinks...I cannot be part of that. So I ended it.
I will always be involved in my son's life to some extent...but with a lover, I won't. My advice is for you to cut all ties with your boyfriend and concentrate on building a new life for yourself. Get out with friends, read, exercise, volunteer, etc., and date when you are ready. But as part of being ready, try to determine why you put up with your boyfriend's behavior for 4 1/2 years, so you hopefully will not get drawn into a similar situation.
Just my opinion...
Best, Susan