You have figured out a lot her.......great news!
Yes she quit her job, cause like him, you and some of us, we are all codies willing to do anything to be loved.
He knew from day one you could never accept his addictions, Deep down he knows he is fundamentally broken so you both always lived with "one food out the door".
He then met someone who would accept him (nothing worse to an addict than to not be accepted because their shame rules them) so he chose to be accepted.
This doesn't make you wrong, this makes you true to yourself.
My ex cheated on me with some crazy married woman with 4 kids who admitted her BPD and who stalked me. He needed someone totally insane to accept him, cause from day one I told him the list of sh&t I would not tolerate.
He was floating, I was floating.
I loved him and wanted a life with him, but on MY terms! I wanted to control him and how he drank etc.....turns out, I didn't have the power to change anyone but me.
So I slowly changed me and he cheated.
He didn't pick booze over you.....he picked his addiction over healing...simple!