I'm not sure it matters. If your partner is neglecting your relationship does it matter why? If his NRE is going to mean that you feel neglected, then his NRE is always going to be an issue and he will either change how he behaves during that period or you'll have to change how you perceive his behaviour during that time.
I agree that you might need to put up boundaries about general information sharing. The sex thing is difficult. Men work a little differently to women in terms of sexual function. I came across a poly guy once who admitted that he has had to restrict sex when he has more than one or two partners to ensure everyone gets some of the goods. That might be easier to tolerate if you know from the offset that a potential or new partner operates in that fashion rather than hearing it on arrival of a new partner but it is still a reality for some people.