Right on, monopepper! (hope you don't mind being portmanteau'd) I'm off to spend the weekend with the poly girl and her other boy, somewhat randomly, at an annual gathering of our friend circle.
He and I were friends before this relationship started, he knows about it and supports 100%, and we've spend some time together already. Apparently another of his girlfriends will be there as well. Ha ha, I am in for some poly-dynamic-observing funtimes. Will report back.
Thanks again, rethinking this via this forum has taken considerable weight off my shoulders and even awakened a tenacious little spark of poly-curiosity in me, it seems.