I have been where you are. You have to quit beating yourself up. Breakups with alcoholics are hell, I know. Especially when the choice is not yours. The feelings of abandonment can be overwhelming. But please remember that the foundation you had built with an alcoholic has crumbled and collapsed because it was never much of a foundation to begin with. It can't be when one or both people are not healthy to begin with. I know it doesn't make it any less painful. I get that part and it sucks. It was hellish for me.
The absolute best way to start healing your pain is to stop blaming yourself for his drinking and to start focusing on your own health--mental, emotional, physical, and spiritual. Let him worry about his own stuff and you focus on yours. When I started to do that, things very slowly got better. It was no magic pill, for sure. Lots of baby steps forward and some backwards, but I got there (so many of us have) and you can too. Please be good to yourself.