Do I get this right.. he had the affair, had angry outbursts in the beginning of your relationship, problematic alcohol abuse, he didn't show any effort to make things better, now he wants back but only if it isn't as awful as it has been for him for the last 2 years if he returns?

Can you read again the post Happyheart wrote March 29th and respond to it, regarding the Harlow-experiment? I'm afraid it is closer to your situation than anyone would want.

Also, reading other threads on the MB forum might give you perspective. I don't know if you have read this one, but I love this thread for inspiration.
Not that I want you to end up without BF, but I want you to recover from the pain caused by the relationship and eventually in a happy and fulfilling romantic marriage. That will require quite some changes and I am not convinced BF is willing to put in the effort.