Hello and welcome.
Some questions first: How long into this new situation have you been up to now? How fast is their relationship developing from your point of view? What triggered your intense responses? Situations, words, actions, ... ?
I was having some really tough months when we needed to sort out all that was required for a actual start into polyamory. It always takes time to adjust, even if you covered the basics theoretically. It mostly feels quite different when you get to the point practically.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.