I think I'm beginning to understand where you are. I suspect it's tied to the fact that we lack the working vocabulary to describe all of our ties to reflect their nature in a fashion that doesn't sound derogatory.
You appear to refer to your primaries as "poly relationships" to denote their importance. Your secondary relationships are different, so you don't want to use the same term for them. Am I on the right track?
And, yeah, "primary" and "secondary" just don't really seem to work for any purpose other than a clinical discussion. I think "paramour" works fine for primaries. I'm still at a loss for a suitable term for secondaries.