It hasn't happened to me, but my husband has gone through it several times.
I thought I'd offer another perspective for you.
It's debilitating to our relationship when he gets all mopey over not being able to spend time with his new interest (in every case he's had the opportunity for at least once or twice a week in person and every day texts/emails).
Because then our time is destroyed by his mopiness.
It's gotten to the point where (I'm the one who is primarily poly by the way)-everytime he meets someone, I just want to go on vacation with our kids and not come home again for a few months.
Because I already know it's going to be him mopey and moody and wanting to be with her.
It's NOT that I doubt his love for me at all and I know his love for me isn't waning. But, he's SO caught up in NRE that he can't stay happy when he's not with them and that makes him shitty to hang around.
When he's in NRE, I miss the times when he is actually FUN to be around, enjoys playing, goofing off, having mad, passionate sex with me.
Ironically, my boyfriend lives with us-and it's never been that way for me. I am ALWAYS MORE interested in fun, and goofing off, playful sex and teasing with my husband when I'm getting that from my boyfriend too.
So, I can't say I understand personally.
Because for me, NRE isn't about a person-but about getting quality time and if I get it with one-I want it with everyone I adore.
"Love As Thou Wilt"