wol,
I hope you are able to stick with your decision. I think it was the right thing to do. I say "I hope you are able" because you are already minimizing how "bad" his drinking is.
As someone who has been in two marriages to alcoholics (one got sober before we got married and the other went back to drinking after almost dying of it), and is a sober alcoholic herself, you are NOT overreacting. Your ex-b/f's drinking is classic alcoholic drinking, and it will get worse and worse--maybe quickly or maybe slowly--over time. He is nowhere near ready to quit, as he told you. I have to give him a tiny bit of credit for not making empty promises to quit--that only prolongs the pain for you as you stand by him, giving him chance after chance that will be doomed to failure because he is only making token efforts to get you off his back.
I have known HUNDREDS of alcoholics--many who recovered and many who never did, and I don't know one person who quit (for good) before he or she was ready to. For some people that takes literally decades of drinking, and, of course, lots of them never get there. And, as soberclover notes, most of the ones who do recover have to suffer losses in their lives before it happens.
I know it's hard to simply forget the "good times" you shared with him. Someday, you will be able to look back and remember those with perhaps a twinge of regret and sadness, but happy you did not sign on for years of misery as he spirals down. For now, keep reading here. It will reinforce your decision to leave for your own well-being. Lots of folks here on this list wish they had done exactly what you have done.