May I suggest that instead of telling her, "I can't".......you begin using two other words that are much more effective with a WW. "No thanks" sounds so much stronger than "I can't".
Throughout this entire situation, you have waited on your WW....hoping her actions would change. Have you considered that it is your actions that need to seen in a much stronger light?
Don't offer ultimatums to a WW. They seldom work. Ultimatums are not boundaries. A boundary would be, "I will not stay in a M of three". If she doesn't make an about face immediately, then you proceed to back up your word.....which is not staying in a M of three.
You aren't going to be able to play soft Mr. Nice Guy and have your WW "choose" you over the OM. You are using the same behavior that helped cause this mess....to get you out of it. How much sense does that make? When you get enough, then you won't worry if you appear cold or angry. And, why should you? When a man has a W who is involved with OM, then he should be angry. I can't imagine not being angry and cold. Those are natural feelings. Don't confuse this with the advice of other interactions with your W.
You are wanting her to make decisions that will let you off the hook of doing something that requires you to take action that may be unpleasant. For example, you are still sleeping in the same bed with a woman who desires another man instead of her H.
I think it's best when the H stays in the MBR and the marital home. However, I have been introduced to some WW's who will physically fight the H in order to remain in the bedroom. When that's the case, then the H needs to consider which is more important......physically separating from his WW and gaining perspective and inner strength, or continue to suffer every day he has to be near her. Clearly, a woman like this does not want to be in the same bed so she can be near him. She feels entitled and uses it for manipulative purposes. Same as not leaving the house, she feels entitled to having the best of both worlds....therefore, she won't leave.
What I'm trying to say here is that you have to make some decisions and show some actions, Pew. So far, you have waited on her to make the decisions......and all she has to say is "no", and you are stuck in the same place. You will continue to be stuck, until you start acting like a man who has had enough and start making decisions on what is best for you, instead of hoping she'll make them for you.
I've tried to tell you what works and doesn't work to draw a WW back into the MR. I am trying to help you save your M, believe it or not. She has to see that you will not compromise your integrity just to have her in the same room/house. She has to see that you aren't afraid to dump her. Right now, she has no worries about losing you. The H who has a WW, has to apply tough love to save his M. Strength is the one thing the WW respects. That's why the H is told to do things that show his inner male strength that she can't manipulate. I wonder if you can't separate that type of strength from a man who is angry & cold.
When I was the WW, I thought my H would love me....regardless of how I treated him. Some people in the position of my H would call that unconditional love. I don't think it exists in M.....nor should it, b/c each spouse should be held accountable for their actions and treatment toward the other one. When we can treat a person so badly without any consequences, it does not build our loving feelings....but destroys it. That's just how bad human nature can become when that person's code of decency is messed up.
So, I think you need to come to terms that you will probably be required to do something unpleasant.....even at the risk of being labeled the bad guy. (However, she's already labeled you the bad guy, so nothing new there.)
It is not about what you feel should work in your M. It is about doing the work that gets the right results. Do what works!