Your answers to your questions are inside YOUR polyship, with YOUR polyship peeps.
What I do not get a sense you have is a solid framework, covenant, or contract (use whatever vocab y'all use) for HOW you agree to be together. Here's how I roll in my poly gamebook
This has not happened yet for you because this polyship configuration has NOT been well defined. That conversation has to happen first.
What is this? A baby "V" with your GF as the hinge with "special occasion" only threesomes maybe? A baby triad trying to grow? WHAT?
But how do I get over this horrible feeling I had that night when I was alone in bed. I want to be able to relax and not worry and allow them their time without the urge to bother them.
This is normal and common enough (to me). You are experiencing what I call polydrop.
The full thread I wrote that in here.
Expect wiggins as your body clears the endorphin highs. Do your poly aftercare stuff.
Learn this about yourself and what it is you need to be reassured.
You are also experiencing Tug of Change. Remember you are in transition here with your relationships with these people. It can feel like Tug of War of the Heart. But there is NO ACTUAL WAR on. It is Tug of Change.
Change is scary sometimes. This new partner person is NEW. Are they from the Muppet Show? Things higgledy-piggedly? Or are they from Star Wars honorable Jedi with good ethics? You are gonnna find out!
So... get your gamebook down for this polyship configuration, and the actual configurtion itself.
What is THIS? How to we agree to be together in THIS so we are in right relationship to each other?
I think addressing these things will help your heebie jeebies.