Different perspective, it's been years, but I can still relate:
He told me one day that he was attracted to men more than to women. He didn't even ever fully confess - but the entirety of that "you and your best friend are different than him and his best friend in comparison to any other relationship I've ever been in before" situation made sense all of a sudden.
I wish I could say "we divorced, amicably [we did], and him and his partner have been living happily ever after [they didn't]".
I'm not even sure it's the cheating that I still fret about, years later. He is gay, I am female - this wasn't going to be a thing! It's the fact that he went on to marry another woman and have two kids with her - and that I know he and the OM are still an item!
I feel guilty both because I haven't told her (we've met twice, we're not close) and because I haven't been a better friend to him (I should have done a better job letting him embrace who he is rather than letting him get married again after he and I broke down over his affair with another man!)
This is such a mess! She's such a lovely woman. He's so definitely not into women. It's not on her (and: it wasn't on me, either).
But he's such a coward! And he's doing such untold damage! I am, literally, the only person (apart from his lovers) who knows he is gay. I am so sorry for his current wife. She probably has no fucking idea. I love him, but he's just being such a dick!