I'm shocked by the fact that STBX plied you with drink.....and then gas lighted you by denying it....and then suggested AA talk to you about your supposed drink problems.

He IS building a case against you - to use socially, and probably with an eye to that hackneyed (but unsettling) ruse - attempting to gain custody/residency of your DC.
He won't succeed, and as you've said, he doesn't want custody. Though he probably thinks he's very clever and original in thinking of it.
I've seen a similar situation from the other side. It works like this: painting the ex in the light of an alcoholic (and worse) makes the abuser look hard done by, with friends old and new rushing to sympathise, and new partners working hard to be 'not like her.' It also makes him look heroic, as he attempts to wrest custody of his 'poor, neglected' children from her supposedly incompetent grasp.
He never quite succeeds. Picture then his dejected slumping and sighing, which brings yet more sympathy. Meanwhile the ex continues to shoulder the main burden of childcare.
Thwart him if you can, thename- keep good records, keep your wits about you, and tell people you trust about what is going on. When it's over, don't keep his secrets. But for now, stay safe. 