I think that if things continue this way it would be fair to ask her to slow down with the new guy and put more proactive energy into your relationship for a little while. I know this whole situation wasn't intentional, but it was frankly a bad idea on her part to start somehing new while things were rocky with you. Sex is a huge part of bonding and loving! She must realize what an emotionally difficult position she's putting you in.
Obviously you don't want to coerce her into bed with you by holding her affections for the new guy hostage, but there's a fine line here... fixing things in your relationship will make the situation smoother and easier for everyone involved. If he's a decent guy, I'm sure he doesn't want to be a cause of strife between you two.
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.