What do I do? This weekend went so well and she's been telling me how much better our marriage has been, but I think that's all just that we haven't gotten into a fight.
Yep. And at least you now know clearly what's going on.
If it were me, without revealing the source of my intel, I'd calmly tell her "I know all about you and _______, and we both know you're lying to me when you say it's 'just friends.' This isn't working for me; I've got some decisions to make."
And then I'd go dim on her, perhaps even telling her she needs to move out.
You did the financial piece of this already; it's time to tighten the remaining screws in my opinion. This is of course assuming that you can't tolerate your wife sexting with other men while married to you and in your marital home.
You have no kids, Rev. Some of us would've KILLED for that kind of clarity and simplicity in our sitches. What took me 60 days to eventually do would've been done in 6.