First - WELCOME!
Second - well, you certainly have the right mindset to make a relationship work, mono, poly, or whatever. A willingness to
1. - explore rather than simply combat the new ideas,
2. - aknowledge that you still have retisence (I liked your "I can muster" line) and issues,
3. - work on understanding those issues,
and 4 - look to others for help and guidance
all speak very well of you as a partner in the marriage. Even aknowledging that you're unsure about wanting to stay is a sign that you are willing to work from your side. Further, you are respectful of her position to at least some degree, even to the point of not revealing who she is until she okays it.
So you're coming from a good place.
Talking about people "being mono" or "being poly" annoys me personally - not you or your words, it gets thrown around here a lot, even by me - but I don't think someone "is" one or the other; they are who they are and they have needs and beliefs as they relate to relationships. At this time, your wife believes that hers are better served in a polyamorous relationship. Brace yourself - that might change down the road! You say that you "are not really sure you are mono". Again - you are who you are, and your comfort and understanding of things will dictate what you need to do; someone who identifies as "mono" might very well have thoughts and feelings for other people, but never be comfortable in a plural relationsip, and someone who identifies as "poly" may very well be seeking something that ends up better fulfilled in a "mono" relationship, or may have some desire to be with one person while never being able to be fulfilled by just one. And so on - as with anything in human nature, it's complex and no two situations/people/etc are going to be alike, tough similarities will exist.
I'm getting long winded. How about I say Third - some questions, if you don't mind?
How long have you been together?
Is this discovery that she's "poly" something new, maybe related to other things going on, etc?
Are your "poly" thoughts a result of the recent issues, or have they always been there and "suppressed"?
That's a start if you'd like input and help...