Maybe I am missing something, but I am wondering what your hurry is in taking action? (ie ultimatum, telling her to make decision now, exposing the A, moving out, etc) Are you thinking that if you move more quickly, she is more likely to end it with OM?
The reason I am asking is because you just talked to her BFF and she said not to do anything rash and she reinforced that W is really on the fence. That appears to be one of the more positive things in your sitch--the minding reading doesn't work--but this is real info coming from W.
Perhaps less is more right now. Maybe instead of focusing on what she is doing and how you can affect that, you should take a step back and detach. You cannot control her or OMs reactions.
You have been clear about your boundaries, that is good. However she has not begun to feel the loss of you. Not suggesting you ignore her or move out, but detach and focus on you. (no pursuing or complementing) I don't see that she has felt that your actions are matching your words.
Perhaps your stated boundaries are more to pressure her to end A and not really to protect yourself.
Just my 2 cents. I really so see hope in your sitch, but I think you are wanting to (understandably) rush this.
-Blu
“Forgiveness liberates the soul. It removes fear. That is why it is such a powerful weapon.” – Nelson Mandela
