Sorry you are going through such a tough thing. However, welcome to the board, there are a lot of good people here to help. Read and read some more.
Most of what you will find here is about you, not your W. Digging deep,inside you and fixing those things to make yourself a better person. Being on your best behavior won't change much. Not saying to be intentionally rude or mean, however 'being nicer' won't do much other than frustrate you as she continues her behavior. It's her choice to cheat, that's cowardly behavior to me.
Snooping leads to a lot of heartache, you already know enough info. How do you see this ending up for you?
Welcome Brother.
Me40; W38; S12; D9 BD11/19/2018 D filed 12/20/18 D Final 7/2020 Being the best example I know how for my kids to see.