I'm going to share my experience with you.
I found out after 8 years and 3 children together that my boyfriend was bi. We grew up in the Bible Belt, raised Christian, even had pastors for grandparents. All that. We'd both broken away from Christianity and religion in general but he obviously still had immense guilt surrounding his sexuality because of conditioning, societal narrative, the culture in this area etc. He did not want anyone to known but he also needed to explore this part of himself, so he tried to experiment in secret by soliciting gay sex on the internet.
He never admitted to anything physical and I do believe him.
Anyway, after he opened up to me about all of it, I was kind of like you, without the hurt feeling - I was supportive and encouraging and we embraced this as something that has brought us even closer together. (I'm bi as well, although I never struggled with it.) We talked about swinging, finding play partners, experimenting etc. Our communication was amazing. We were closer and happier than ever.
We decided that we love each other and want to spend the rest of our lives together (just as before) but we were honest enough to admit that, as humans we only live once, and we didn't want to hold each other back from fulfilling desires. One rule - we talk about what we want to do first. We communicate about it. And go from there.
Fast forward a few months and I caught him on a dating site pretending to be single, setting up coffee dates with women, soliciting nudes, exchanging nudes, asking what it would take to be FWB with others. Being generally sleazy.
I found out about it a week before I told him I knew. He was never going to tell me. He was trying to be secretive, again, after all the growth I thought we'd had.
We're trying to reconcile and are still together. We have small children and I am a SAHM. But I'm miserable. I can't bring myself to respect him anymore. I don't adore him like I used to. He is not who I thought he was. He's a liar and a cheater and he's selfish.
So, yeah. I hope your partner is not like mine. But secrets are secrets. Dishonesty is dishonesty. Circumstances don't really matter (like I used to think they did).