It's hard to come on here and tell you what you should and shouldn't feel. It sounds like using your own logic hasn't done much for your situation. But i want to give you props for really recognizing where you are and how you are feeling. You are owning the situation and that says a lot. You clearly love her and want the best for both of you!
I think your fears/insecurities are valid. They are a part of who you are. Sometimes feeling guilty or hiding from them will only make it worse. Poly to me is about allowing personal freedom with your emotions (to be free to love more) Instead of focusing on how bad you feel, try some exercises with your love. What makes you feel good about the situation. What are some good qualities you have? What are some good qualities these other men have? Don't overwhelm yourself by trying to make it better all at once, take baby steps.
It's important to keep your communication with her open about this too. Sharing with someone so close to you can sometimes help you relax a little. Remember you are doing this together.
Have you had experience in the bedroom with another man there?
"It is a truly wise man who does not play leap frog with a unicorn”