sorry i had to read that 3 times!
are you the dad?
if so yes you have done the right thing, the baby needs looking after by someone properly and soba!
you do need help tho, i mean legal help,
are you on good terms with the mother? silly question i guess,
but..... maybe trying to talk and reason with her, making her see the baby being with you for the time being is best,
i cant give u loads of advice as i wouldnt know about these situations, tho i do strongly feel you have done the right thing,
a drunk mother past out, is no good to a 12 week old baby!
good luck xxx