My unsolicited advice is, for your own self-respect, leave him. It's one thing to forgive a partner who has a one-night stand. It's another to stay when he's turned cheating into a lifestyle. You've also got to ask yourself - would you want your daughter to be in your situation? Would you want your son to treat his spouse the way your husband treats you? What kind of example are you setting for your children?

You can make the divorce as painless on your children as possible, make sure their father has generous visitation rights and don't get caught up in petty crap during the divorce. JMHO.