hi formylose, I'm glad you found this forum too. Sorry for what brings you here, of course.
Well, you wife does have a big drinking problem and probably is an alcoholic.
The first thing I would recommend is that you research alcoholism, find out as much as you can about addiction (for you, not for her). I would suggest you speak to a lawyer about the situation and possibly separating. Just because you want custody of your child doesn't mean you will get full custody (doesn't mean you won't either!). Ask him or her what kind of proof you would need, if sobriety testing could be part of the rules for visitation. Start a journal of her drinking and when she is out and when she comes back, it may help you later.
You can't really help her unfortunately, she will quit drinking when she is ready to. She probably doesn't remember much of what she has done on her nights out, being black-out drunk will do that, but I'm sure she remembers where she woke up, but doesn't share that?
I don't think there is an easy solution.
It is never really easy to separate when there is a child involved, however you also don't want your child to grow up in a house with an alcoholic. I'm sure you already know that alcohol will be in the breast milk the baby is being fed as well, if she is drinking that often and is feeding the baby within a few hours of that.
If you know this is a bad environment for you and your child then you just need to keep taking the next step and doing the next right thing for the two of you.
I wouldn't wait around for her to get sober. I mean she might do that tomorrow, or 20 years from now, but hope is not a plan.