My household is sort of a triad. Three of us who are all fairly equally partnered, in different ways. I think for us, our primary relationship is as a family, rather than any configuration of pairings within the group, and each of us is open to other relationships as they tumble into our lives. D does have a regular 'secondary' friend with benefits, and I have one or two playmates, but my primary relationship is to my family.
“Great things are not accomplished by those who yield to trends and fads and popular opinion.” -Kerouac
I'm R (male), I live with D (male) and L (female) and L's two kids.