I like that validation technique with a twist idea and will definitely put that one in play. With the financial stuff I'm pretty confident she will say something along the lines of "if I have to pay for all of that then how will i live and be able to support our daughter?" That's pretty much how I think that one is going to go. Any thoughts on a response to that?
"I agree, this is going to be difficult on all of us."
if pressed, then:
"I think we can both agree that D's needs come first, and she will be well taken care of. What WE need to do is figure out an equitable distribution of our monthly obligations. I will continue to more than help take care of the family's NEEDS, but I have decided that I am no longer willing to pay for anything that directly enables your affair."
Have you figured out in what other ways the family's (your) finances are being used to either directly or indirectly pay for her dalliances?