Trust me, I wanted to throw my wife out too, but the idea is for them to have a period of time -- say 30-180 days -- in which to see the "new you" living your life out in front of them, and shining a path back to the marriage.
Eventually, if they don't give up their affair, you do have to either throw them out or file for D, to preserve your own sanity and your own self-respect, but by not doing it right away, you give yourself a chance to live the "better you" in front of them, and to have THAT be the last thing they remember as they ponder their life-altering choices.
