Hi Petunia. Your situation sounds very tricky and very stressful. Compounded by the stress of an impending marriage. I share some of your issues, in that my wife is in the throws of NRE with our GF, and I have struggled with envy and jealousy. I am proud to say that I have come leaps and bounds from where I was. I think all the advice you have been given is very sound and intelligent. Here is my two cents to the conversation:
I finally had the realization that I was so wrapped up in my own fears, needs, and wants...along with my desire to maintain the power I have in my primary relationship, that I was making myself an emotional basket case. I have all those issues of envy and even jealousy because I do not have the same intense relationship with our GF that my wife does. But you know what? I became so wrapped up in my own shit that I did not stop to think or consider the needs, wants, and fears of the other two women in my life that I love. The reality is....I wan this poly relationship...this triad. And if I truly want it, then I have to remember that there are three individuals involved with their own needs and wants...not just me. Yes my stuff is important, but it should not be the focus of everyone else all the time. I am in primary in this relationship, but my two loves deserve equal consideration. It was time for me to stop being so self consumed.
Now, I realize that your relationship is more of a V, but still....in a poly relationship, everyone needs to be considered. Maybe there is a way for the three of you to discuss your wants, needs, and fears together in order to negotiate some sort of agreement that works for all. As far as the NRE goes....you are going to have to roll with it. It lasts as long as it lasts. If you really want and trust this relationship, you have to be willing to ride it out. Eventually, things will cool down enough for everyone to find balance again. Definitely voice your concerns and your needs....but at the same time....ask your fiancee what he needs and wants. Sometimes in dealing with our own anti-compersion, we forget to check in with the other person/people. You might be surprised.
Either way....I wish you luck and I hope you guys work it out.