Get some counseling. Talk to an impartial professional about an exit strategy from your marriage and about why you're putting all your self-esteem eggs into a highly unstable relationship basket.
Oh and if you think your kids think everything is hunky dory, think again. Unless they are very small (as in under age 3 or so) or severely disabled, children can sense when there are problems in their parents' relationship. Don't kid yourself that you're staying together for their sake. They know there's trouble.