No Way Out

What you've done was very bad, and you must face the consequences in some manner. Either you can tell your partner, adn watch the look on their face when they find out they were betrayed...or you can keep it inside forever, always horrified of running into the person you did it with when you're out as a couple. Hey, face it, you screwed up...I did too, I've been keeping it secret for over a year and it's really no good.