Sending big, huge, enormous hugs your way. Of course it hurts. He was doing okay, you believed him, you wanted to trust him- it's human nature. And now you are recovering from a major surgery, have a newborn and have no help-- actually it's like you have 2 newborns.
My AH went downhill fast when D3 was born. I saw anger and irritation from him that I never had and his drinking increased a LOT and it was of course my fault and the baby's fault. D3 has remained a high maintanance, unable to self soothe child and I am sure it is because of the handful of times AH got to her first during the night and yelled hard at her (as a week or month old baby) to "f'ing stop crying". I didn't leave then and am not sure why and wound up with severe severe PPD so I wasn't really capable of making any major life decisions for a while there...
The fact that you are connected on here gives you more of a support network than I had and I hope that this, al anon, therapy? are enough for you to be able to give yourself and your sweet baby a better life asap than the one I subjected my baby to.
I am not judging at all or saying "you should". I know how devastating it is to think "this time he'll stick with it" and have it not happen and I know the feeling of saying to myself "I shouldn't be so upset- I should have expected this" and then being all the more upset bc despite "knowing better" I AM upset.
Let yourself be upset, and hurt and feel what you feel. You have done nothing wrong. You are being held hostage by someone else's disease and you have a ton on your plate right now. Be gentle with yourself.