First of all, it's not impossible to be in NRE with 2 people at the same time. Of course, unicorns in triads can feel this. I also felt it, not as a unicorn, but when I had been with my current gf for 3 mos, I met a guy and had NRE for him as well.
Love withers under constraint; its very essence is liberty. It is compatible neither with envy, jealousy or fear. It is there most pure, perfect and unlimited when its votaries live in confidence, equality and unreserve. -- Shelley
There's no lying in polyamory!
I'm a 58 year old woman with 2 partners:
miss pixi, my live-in gf, 36 (together since Jan '09)
Ginger, bf, 61, married, lives nearby (together since Jan '12)