I'm also a GG.
I found out by accident. I found women's underwear that I knew weren't mine, and I was pretty sure that he wouldn't have some other woman's underwear. He confessed that they were his and he had been dressing in private for years without my knowing. I was totally okay with it, and we plunged in headfirst. A couple years into it, I have a more difficult time with certain things, but am very willing and eager to get us both to a happy place.
I believe I would have had the same reaction if he had openly told me on his own rather than having been sort of forced to out himself.