IMO, a person can't love a person they don't respect. Before a person ever learns how to love another person they learn how to respect them. Respect births love.
On the other hand a person that loves themselves will not allow another person to disrespect them. So by allowing another person to disrespect you, you are basically telling them you dont love yourself.
So first you start loving yourself, second you state your boundaries, and lastly provided consquences when your boundaries are crossed(tough love).
Lastly, you need to look at your Sitch objectively, look at your Sitch from the outside, how would perceive yourself? If your W found out you knew all this time and didn't say anything how would she view you?
You are absolutely right you can't control a WW, but you can let her know you won't put up with her sh!t and manipulation. Let her know she is not as smart and sneaky as she think she is. Become her H again and light tower.
Oh and don't ask her about the A, if you have proof, present it to her and tell her you know she is in an A. Leave no room for her to wiggle or manipulate out. Tell her you won't be a M with 3 people, and start moving forward with your life.
I know I said lastly, but you not telling her is driving you crazy.
Sandi, also gave you some sage advice about your Sitch. She want you to start living through actions and not words.
So, Sandi, can correct me if I'm wrong, you gave MBE actions for the week, don't discuss the A, with your W. I think it's totally different than presenting the information and making his statements and leaving it at that. No discussion involved in that scenario.
So if you ask her about the A, it becomes a discussion, if you present the proof about her A, and leave no wiggle room, it becomes a statement. And dont let her draw you in. You present the info, you state you wont be in a 3 person R and get up and leave.(IMO)
M:37 W:37 T:11 M:10 S17, S13, S10, S4 BD:06/28/17 OM confirmed 07/20/17 Recon the M 10/29/17 Working hard:2gether
Onward and forward
This process is not a sprint it's a marathon! Patience, Patience, Patience.