NRE typically lasts between a few months and a couple of years.
However even if it turns out to be on the short side, I would advise against bottling up and hiding how you feel. Talking about it doesn't necessarily mean you will limit their relationship. It's possible that instead, you will figure out things to do about YOUR relationship that will make the NRE tolerable to you, because you won't feel as neglected.
I think you should mention it, not in an accusatory way, but in a "hey, I have these feelings, what should we do about it?" way.