Just from my personal beliefs I have to say what you're wife is doing is a bit unfair. While marriage is complicated and the bond is very important, to say you're holding her back as a person is not quite nice to say. The only person holding her back is herself. She could leave you if she truly wanted to be "herself" and for her not to acknowledge your feelings as well is a little selfish(but there are two sides to every coin so hear me out).
My husband and I slowly have been developing the idea about polyarmory with him, and he's known I've always believe in the ideals of polyarmory. (Since I was about 16 after dating around for awhile). Maybe it's because I'm polyflexible and can let myself be in a monogamous relationship for the sake of the ease of mind of my spouse. Perhaps she can't be polyflexible, so I can't make full judgement here, as everyone, IMHO, is different.
Best advice I can give you on your own feelings is understand why you feel jealous. How are you supposed to deal with something when you can't put into a sentence, "I feel jealous when she talks to men because....?" Do you feel you're inadequate, because she seeks other relationships? Do you feel like you have ownership to her? Or do you feel it's deep seated in societal norms that being with one person only is the only right way and what shes doing is wrong? Do you feel she'll love you less, because she loves another?
Once you end up with a good explanation(s), then try to weigh pros and cons. Example: I feel inadequate. Talk to your spouse and tell her how you feel. She'll most likely try to reassure you that you're not inadequate. That most likely won't be enough, so discuss with her on how she can take the responsibility of meeting your needs, since you've agreed to allow her more freedom, meeting her needs.
From what I've read, you keep saying how you can stand it when she gets close or talks to another man. But WHY, why does it bother you so much? That's a VERY important thing(s) to understand to begin dealing with your emotions. And talk to her about everything. This is something you're going to have to work with her through if you decide to stay with her while she wishes to be polyamorous. Her adding a new dynamic to her life, will affect your relationship, so she should take responsibility to work on the relationship with you. But try to be open minded and understand a few things. Such as: She most likely will not loose any love for you. Love does not have a quantity, but rather you work to insure the quality.