Try counseling, individual and couples. if you wnat to keep your marriage together, you have to be open about trying different things to keep it together. Something was being said or done by either one of you that was not listened to. when he says something toyou that you don't like, your defenses go up, but he's saying it for a reason. And vice versa. Whoever should take that and learn from it. Most people don't though, they just shut down. As long as you feel like you tried everything to save your marriage.
If it does go as far as a divorce then as far as the child support, I think try to keep it fair. i know easier said than done when you feel he's the biggest jerk. Try and calculate the cost of living for them and then a little extra for the just in case moments or whatever.
As a child of divorced parents....it sucks, especially if the parents don't get along. If i learned anything from my parents divorce and from watching my friends with their divorces, is that regardless of the circumstances, you have to try to make an effort to get along and be in the same room together for the sake of the kids. It soo hard when I know that one or the other of my parents will not come to an event because of their relationship, or its so tense in the room that you don't know what to do with yourself. you have to think of whats is in the children's best interest because this is for the rest of your lives and thier lives and their children's lives....forever. Thats alot of school plays, graduations, birthdays, weddings, births, etc.
Do what you have to do and ask for what is deserved and needed for the sake of the children. this is one of those situations where you're gonna have to be super grown up about it and do alot of pride swallowing. It WILLl get better.