And this is the dark side of cuckolding. It sucks when it turns out that you and your spouse don't share the same sexual tendencies, or one develops some that the other doesn't like.
I do feel for you, man. But I have to say the same that others have said on here. If you yourself are not happy with the situation, and feel like it's something that you don't want to explore, then you are entitled to that. There have to be some sacrifices in relationships on both sides for them to work, true. But everyone has their lines that they absolutely won't cross. Is this whole situation one for you?
If the answer is no, then you two will have to work something out where all parties are happy. But if the answer is yes, that an open relationship truly isn't your thing, then if she isn't willing to change her stance, or if you can tell that she'll truly be unhappy if she has to be monogamous, then it's possible that you two have to part ways.
It does suck, and having grown up in a split household I hate divorces with a passion. But sometimes, it is what is necessary for the happiness of both and for both to be able to move on and live their own lives. So in the end, this isn't something that anyone else can answer for you. You have to answer it within yourself.
Sorry for the long post, but I hope in the midst of all this I said something that can help you a bit.