My cheating was about 18 months into the relationship. It was a ONS. I never told her until her cheating came out.That changes things since it seems you both have had the same thoughts about your relationship. And you two have something in common.
You just need to decide do you want to try and R with her or are you done.
I mean she just found out you cheated as well. It doesnt matter at all when you cheated, the fact you just told her, to her it feels like you cheated yesterday.
So you both have a lot of talking things out if you want to stay together.
If you want to stay together, than you and her need to talk. And she has to understand that the things needed for R. And that does mean NC.
Are you still in contact with the OW?