Welcome to SI, the best club nobody wants to join. In the JFO (Just Found Out) forum, there are some posts pinned to the top that we encourage new members to read. There are also some with bull's eye icons that have some great information. The Healing Library is also full of information, and includes the list of acronyms we use.
If you can, IC (individual counseling) with a betrayal trauma specialist can be very helpful. If you're having trouble with depression, anxiety or sleeping, you may wish to ask your doctor for some meds. They can be helpful in the so, so painful beginning of this. Also, you may wish to be tested for STDs/STIs because there are some nasty diseases out there. Please don't have sex with your WW (wayward wife) until she is tested and shows you the results.
Don't try to make sense of what she's doing because it doesn't make sense at all. It will make you crazy. There isn't a way to understand it. It's common for cheaters to rewrite marital history and blame the BS (betrayed spouse). It isn't anything you did or didn't do, say or didn't say. She has made some crappy decisions and the A (affair) is all on her. She had a lot of other decisions she could have made, like talking to you, asking for MC (marriage counseling), asking you to help with whatever, D (divorce) - all without cheating.
There have been some members who remained quiet about it, then served papers and walked out the door. Be sure to check with a lawyer first, as you don't want to "abandon" your daughter or the marital home. Some lawyers have free initial consultations...and if you see them, she can't use them due to conflict of interest issues. So, the more you see narrows her pool of attorneys to use.
Sorry you're here.
BW M 34years, Dday 1: March 2018, Dday 2: August 2019, D final 2/25/21