I am one who found out years later. WH had denied, gaslighted, and convinced me I was crazy.
He finally admitted it last year.
It may have been years ago (in my case I think there has been more betrayal since there but that's a different issue) but it is new
to you. Like it just happened.
Looking back on things, I examined behaviors I thought were odd, and interactions that were unhealthy between WH and me. WH knew, I didn't. He reacted in his life and towards me in ways that were dismissive, blame shifting, aggressive so that I would not question him. All defensive behaviors. It colored my marriage and I wasn't aware why things were "off". I do now, and I am reviewing my life.
I'm writing this to you because many of us have (do feel) as you do and I want to say it's normal. It's a shock to you and something you now have to process. That will take time. Don't let anyone try to tell you it doesn't matter since it happened a long time ago or that you should just move on and forget it. Take your time to process and heal.
Reading the library here, and in the forums has helped me greatly.
Best of luck to you, and please know we are here.