How should i go about divorce and child custody?

my wife(common law marriage) and I have 2 baby's, recently she got caught cheating, and needless to say we are not together anymore, she told me that she don't care if i take the kids that we're just a burden to her, and even agreed to sign the form to relinquish custodial rights, but my issue is that she all but emptied out the bank account, and because of her "encouragement" i've been the stay at home parent, and i agreed because i'd rather that my kids grow up with my morals and teachings rather then a baby setters, , so now i'm without a job, she's left and is staying in a house that's known for drug usage... how do/should i got about getting a divorce, getting financial help, and getting full custody of the kids, because i know if i get state istance, that they will go after her for child support, and that she then might change her mind to avoid the child support, and more then anything i want my sons, and i will do whatever i have to, to protect them and keep them save, and i know it cant happen with her