In any relationship, but *especially* in poly, where feelings can be so complex, partial honesty is not significantly less hurtful than full dishonesty. Either way there are lies happening, even if only by omission, and that can really damage people and relationships. Then again, it doesn't sound like your relationship with this guy is emotionally authenticity enough that it even matters? There *are* great men out there, I know a number of them... don't settle just to be with someone, anyone. Why not dump this guy and just see your gf?
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.