This whole custody issue is something that keeps me up at night as well. I want to leave my Wife, but I know she would fight tooth-and-nail for full custody, and possibly get it because she's the Mother. Thing is, she drinks too excess most nights and when/if he wakes up and cries, she can't hear him because she's passed out snoring on the couch.
She admitted to the marriage counselor that she 'did' abuse alcohol, but I'm not sure that would be admissable. So, I'm just keeping a log of her antics and consumption, and waiting for the next big f-up, then I'm going to a lawyer. I don't want that dear, sweet child anywhere around her.