Do NOT tell her what you know, and what you don't know. Say only "I know all about you and ______, and it needs to stop, immediately. It's incredibly disrespectful to me, to our marriage and to our family." By not telling her what you know specifically, she will have to assume you know EVERYTHING.
Tell her nothing more than "I do not want a divorce, but make no mistake -- I am not willing to live in an open marriage. End your affair and come back and work on the marriage with me, and you will find that I am ready and willing to work on all issues, including my own, as I've already been doing as you know."
Then end the convo, and remain distant and mysterious. The phrases "I'm not sure how I feel about that" or "Sounds like we both have some important decisions to make" are your friends.
More later, gotta go to an appt . . . how you handle this is a CRITICAL step, shodan. Make sure you post here first without doing anything drastic or getting into any deep convos with her!!!
