I think it's easiest to keep it simple, saying something like, "There are a few important people in my life, and we love each other, but we're not exclusive or traditional."
nycindie, that's perfect. I wish my brain had a speed dial to your advice line.
Your suggestion reminded me that Ocean came up with a cool description the other day: "inclusive" (as in, not exclusive). I like it very much, though it's more of an in-joke than a concise way to explain our situation to other people.
(Incidentally, I also like "cryptic" as an alternative to "queer" - an idea that I stole from straight/cryptic crosswords. Again, a label that's perhaps more fun than useful)