NRE has never prevented me from focusing on another partner. You still spend time with others, and it seems to me it's not respectful to spend that time talking about how much you love or want someone else. I mean, mentioning it is one thing, but all the time? Enough that it distracts you from the person in front of you?
I think he needs to learn to push that aside and focus on you during your planned time together, snuggle you, have sex, everything as normal. If he can't do that, if he can only focus on one person at a time... it doesn't sound to me like he's poly.