Still, your W is doing the same thing to you that those older boys did when you were a kid. She is a bully. That is why you shut down with her. That's why you won't say "no" to her and will do whatever she says. Bet you get that same sick feeling that you had as a kid.
She has to have you stand up and tell her "no"! She needs that! She desperately needs to respect you, b/c otherwise there is no way she can have those "in-love" feelings for you. Respect is the lifeline for a woman's love.
She needs to see her H doing what he said he'd do, or what he wants to do, or what he knows is the best to do...in spite of what she demands. Oh, she may throw a heck of ait, but she still needs to see her H being the man she M.
She has treated you badly. She went back on her word. She tested you to man-up and stop her, but you didn't. You thought letting her have her way was showing love for her....but it isn't. Now, she's showing (or about to show) the ultimate disrespect by having an A.
Considering the background, you will have to prove to her, more than once, that she cannot treat you like a doormat.
Have you considered why the boss's W has suddenly started working PT? I'm sure this is not the first time he's chased after skirts. She may have had a little talk with your W.
You will have a lot facing you, but you have what it takes for a woman to know she doesn't want to lose you. Also, your son needs to see how a man needs to deal with a rebellious wife. He needs a role model in order to know what a good MR looks like and how a man gets it.
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!