When you confront your spouse for cheating, it is a negotiation, and consequences are your currency. Your spouse needs to know the PRICE he is giong to have to pay to keep the affair going.
The confrontation is where you prsent him with "the bill" for continued promiscuity. The bill itemizes the consequences he brings on himself should he choose to continue.
AND, you present him the more desirable alternative
End the affair, and I tear up this invoice right now... its an easy choice if you play it well
How about this one? I'm thinking I should do this tonight, but then I lose the element of surprise if I can't get a hold of OWH.
"I have decided that this isn't working for me. I will not live in an open marriage, and have you lie to me about it. I know all about your infidelity (changed from you and OW), and it's incredibly disrespectful. (added->) You are hurting me, the children and your family. I value myself and our family too much to keep doing this. I want to give this M my all and see if we can revive it, and that's impossible with a third party involved. I would like you to choose to end this affair and give our M the chance it deserves. I would like us both to be able to hold our heads high and say we were honest and did things the right way, regardless of what the outcome turns out to be."
If there's an opportunity for discussion after, I'd like to add "You said last night you were scared. Well, I'm scared too. I'm scared you will not give this a chance and throw away years of love and passion because we both hurt each other. I'm scared you won't let yourself forgive me and accept my forgiveness so we can move on and build a new marriage out of the ashes of the old one."
