Yeesh, all this on again off again stuff just sounds like a lotta drama. If you really want to continue with her, I would suggest making an agreement to not talk about Guy on dates, and to keep talk about her with Guy to a minimum as well. Just step back and let them get back together or stay broken up on their own terms, without you as any sort of middle-woman.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.