It was wrong and hurtful of him to keep comparing you to her and asking you to change. Like, really, that's messed up, he should apologize even if it's happening less now.
That said, I don't think you can justifiably ask him not to do this. Like, poly is ok except for with the one girl you love more than anything? How could he NOT resent that? All you can do is absolutely require that he show respect for your relationship (not cancel preexisting plans to be with her, not give her gifts and favors while not doing the same for you, etc), NEVER compare you two like he had been doing (so not cool), keep you in the loop, and commit to doing things that make you feel special, valued, important, etc.
I'm concerned that he won't be able to hold up to those things, because of his behavior in the past. But if you want to give him the opportunity to prove himself, to prove that he can do poly in a healthy, balanced way, that is the list of requests I'd recommend.
The major players. Me, 30ish bi female. Gia, girlfriend of 4+ years. Clay, boyfriend/dom. Davis, ex/friend/"it's complicated." Eddie, roommate & fwb.
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. Liam, Eddie's husband.