Let’s see: agree that the marriage is over. CHECK! Tell the kid(s) CHECK! Move out CHECK!
Find a lawyer. Do you even know what kind of divorce you want? Are you going balls to the walls, take no prisoners, adversarial divorce, and end up in divorce court with a posse of expensive suits on both sides? Are you going to try mediation, where you both sit down to talk about it with a third party and try to come up with a solution the courts will like? Or will you go for a collaborative divorce, trusting your partner completely, and have no courts involved?
And if you can’t afford a lawyer, don’t despair. Try these folks on for size.

LOL thanks, Angel. I have no idea how to start.
i wish i could give you advice… but i’ve never been there so i’ll pray for you instead.