Well, although I am very inexperienced in poly relationships, I have had an experience similar to yours. I think it is good you are looking into what you are really feeling, and why. Jealousy can be overcome. I know that as fact because when I started out with my expartner, I was programmed a jealous person. It seemed to fade away when I started acknowledging what was really important to me in my relationship, and why I loved the woman I love.
The suggestions I was given by people in this forum were to figure out exactly what I needed to feel loved, respected and secure and communicate that to my partner. To communicate with her about my feelings and hers whether they are comfortable or not.
Read up on New Relationship Energy (NRE) and talking to your partner about it and your feelings around her NRE. I found in my relationship that my partner was pretty much blinded by her NRE and could not manage to maintain any sort of presence in our relationship as she was always distracted. What would have worked for me is if she could honor the relationship we had created by being present when she was with me.
All that said, you will find many good reads on this site and suggestions. One suggestion I received was to check out the book "Opening Up: A Guide to Creating and Sustaining Open Relationships." It speaks to a lot of subjects and mentions things that probably and might arise in a poly relationship. Suggestions of what to discuss with your partner.
You're in new territory for yourself there, I would try to figure out what you need to feel secure, loved and respected, then communicate that with your partner in a way that is not possessive, angry or in a way that feels like "you owe me this." Because those vibes are deal breakers.
Anyhow, this is just a bit from an inexperienced fellow, but I hope some of it is useful to you.
Best of luck to you in your new journey.
"You can't make a giant just by stretching out a dwarf. One person's beauty mark is another person's wart."