If she says something like "I'm not even sure I WANT us to 'work' right now, so why should I listen to anything you have to say?", say
"You don't have to -- you're an adult, and you're free to make your own choices. Whether or not to work on our marriage is certainly your own choice, and I can't make it for you or even tell you what to do. What I CAN let you know, and I certainly WILL let you know, is under what conditions I'm willing to remain married to you. And having an open marriage, with a third person in it, is totally unacceptable. If you refuse to end your affair, then I cannot remain married to you."
If she says "Are you saying you want a divorce? say "I don't want to divorce. But I'm not willing to live in an open marriage, so I guess we BOTH have some decisions to make, don't we."
The key to "boundaries" vs. "control," as I wrote to you on your previous thread, is to make the choices HERS, but to let her know what YOUR boundaries are and that there will be consequences if she crosses them. It's a calm, loving, yet firm expression of basically "Hey, what you do is up to you, I can't control you. I'm just telling you what I'm willing to put up with, because it's only fair that I let you know."
Adding in a "and please don't take forever to decide, because my patience isn't infinite, and your recent behavior is making me lose my love for you" is entirely bonus/optional.
