It may be possible to move to something less isolating-feeling without forcing a triad. For instance, if you and the other wing were friends, then both he and G could go with you, at least sometimes, to those parties where you miss G. Or you could all three go out for dinner. Or, perhaps, at least one night a week, without it being a sex thing, you all could sleep in the same bed, with G in the middle. Maybe in time you could all three live together (NOT saying you should rush into that, but in time) in a new, bigger place. Phy's blog provides a great example of a functional live-in vee.
Just some thoughts. I really do think togetherness is generally the only way that co-primaries (which is what it sounds like you two are to him, what with him spending several nights a week with each of you) can co-exist long-term. One big team, even if it's not a triad. "Brother-husbands", if you all ever wanted that level of commitment.
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.