In my triad relationship, my male partner obnoxiously insisted that both I and my wife bear children. I broke up with them for many reasons, but that was the last straw.
My last partner and I were both pretty clear about not wanting kids at all, ever. Our disdain was manifest throughout the relationship. Some fifteen or sixteen years into the relationship, he was pushing forty. I was tired of pumping female hormones into my body (via the Pill). I worried about long-term use. I suspected that the Pill messed with my moods, and I resented the Pill's implication that I was female. (I was back in the closet by then and had issues.) Anyway, since neither of us wanted kids, I asked him if he would be willing to step up to the plate and get a vasectomy so I could stop taking the Pill. I couldn't use spermicides and stuff, and we both hated condoms.
He suddenly backpedaled and said that he wanted to keep his options open. If something happened to me, he said, he might find another partner and want kids with her.
Yeah, right.
Just be honest, man. You don't want to get snipped. I probably wouldn't either. But don't suddenly pretend that you're interested in children when it's quite clear that you aren't.