Good luck with everything, meinsb. Ultimately, I broke up with my husband, but it was for a variety of issues and not a result of polyamory. I do still wish I could have been upfront about being polyamorous from the time I met him, but I didn't know about polyamory back then.
I believe you can work through everything. Be honest, communicate a lot, try to explain your point of you and understand hers. I don't know your specific situation so I don't know how it will turn out, but I don't want people to look at me and think it means coming out as poly is doomed to break up your marriage. Lots of other people have stayed together and made it work, including mono/poly pairings. And I don't believe the mono/poly aspect caused our marriage to deteriorate, as I wasn't aware of it. I think if he had been poly, like I thought he were, we would have separated nonetheless.
But lots of people who are both mono break up, lots of people who are both poly break up. It happens. I hope people can learn from the mistakes we made, while remembering each situation is unique