Often in affairs there is something called gaslighting that occurs. The person who had the infidelity is trying to play down the impact from it and the other person is trying to believe it (I think it happens with addiction also....but it is more often used with affairs). It is based on an old movies of the same name.
There is a rollarcoaster of emotions that this stuff brings up. What helped me was getting support (Al-Anon, Therapy (both individual and marital...which became individual after a bit too), here, reading, and it was all I could think about for awhile).
In addition I relearned about the grief cycle. Denial, bargaining, anger, depression and acceptance. Knowing that what I was feeling was normal was incredibly helpful to me, because I did not need to beat myself up about this any further.
Janis Abrahms Spring work on affairs helped, "Not Just Friends" by Shirley Glass.
For me (it took awhile to get there) No contact = No new hurt. That was challenging in the first few months.
Hugs and take care of you (even thought it feels contradictory right now).