The best advice is to get EXPERT advice before confronting or even hiring an investigator. You are in for a potentially very long road no matter what you do, and you want to give yourself the best chances for success and happiness. Of course the experts we recommend are Michele and/or the DB coaches, but the board is NOT expert advice. You may have a promarriage counselor nearby that can help you.
If you confront the OW (and if you tell other folks like family or friends) you set something in motion that you can never reverse.
Before you do ANYTHING, know YOUR goals. THEN figure out what you need to do to achieve your goals, not just react.