This is esarati's wife. Figured it was time to jump in and bring it back to the question he actually had.
The problem isn't that he's having trouble finding another partner of his own. It's simply that he feels left out. I am aware of this, and I'm doing everything I can think of to minimize that feeling, but we're both very new to this sort of thing. I made a point to have them meet each other, I keep him as informed as he's comfortable with, I make suggestions for him on how to fill his time while I'm away, and we've talked countless times about the situation, how he feels about it, and what I can do to help him adjust. I'm actually the one that directed him here, in the hopes that you would say exactly what you did, that being fair and being equal are two very different things.
I talked with him at great lengths before I began to pursue this, and truthfully I never would have allowed anything to develop between the other man and I had my husband not given his okay. Once he realized that it wasn't just a one night fling, though, he backtracked, telling me it wasn't fair for me to leave him alone to spend time with this man, even as minimally as I am (I've only seen him once a week since this started). I told esarati I was okay with him trying to find another partner too, but he just tells me I would be too jealous if he did. I admit I do feel a little jealous when he spends time away from me, but not once have I let that stop him from doing so. I encourage it. I think it's healthy to have lives outside of each other, friends and interests and activities that aren't always shared between us. He thinks these are just justifications to get what I want.
Is there anything I'm not doing, or missteps I'm making here that I can correct? I really don't want this to distance him from me.