"To Thine Own Self Be True"
I don't know what that "looks like" for you, but when I stray from that common precept I am harmful to myself and others.
Something I heard once is if I tell the truth it's no longer "my problem", I have found that to be true, I just needed help in finding out what the truth actually was.
I had to work a 12 step program (1.5 actually...never mind lol) get a sponsor and do some therapy as well as "do the reading" to begin to get an idea of who "my own self" actually was, but for me, when I stayed in a relationship I wasn't 100% committed to I not only harmed myself grievously but I robbed this woman of any chance of finding someone who would give her what I wasn't.
I am by no means recommending any course of action other then "to thine own self be true" but from "here" it appears you already have your answers just are having difficulty with the "resolve".
This is purely speculation and opinion but from here, if you were to use "her drinking" as an excuse to leave it wouldn't be any different then her turning the tables about "your supposed infidelity" they both appear to be tactics to draw attention away from the "core issue", I had to be careful to not leave in such a way that I was "the Good Guy" which is of course what I did, I just regret that now.
I am still very close friends with the woman I did that to, and we were talking yesterday, she was telling me how much she would actually liked to be married and have someone in her life full time, and I can't help but think she actually might have that person in her life had I left her when I realized I wasn't a "perfect fit", she has been single since we broke up 2.5 years ago, I probably realized I wasn't "a perfect fit" maybe 6 years ago.
I feel I absolutely stole those years from her in a way although we had a very nice and loving relationship, somewhere deep in the depths of my heart I think I knew she wasn't "the one".
P.S. We have absolutely discussed all of this in subsequent "exit interviews" she knows what I did and why I did it, and we are still "best friends" but the truth is ..... I feel bad about it sometimes...I wish I would have handled the situation with a little more integrity.