Drop it. If you are married and no longer wish to be with the person you chose, leave them first. If you have children, it might be wiser to suck it up and stay with him for them. Cheaters suck, don't become one. Settle your differences first, then move on. But move on to someone not married, don't be a homewrecker. As was said earlier, she will ALWAYS be the mother of their children, etc....