Well, I'm married, have been 18 years now and have a boyfriend that will be of about two years this August. So my relationship with my hubby I call primary. We pretty much agree that it's more to do with how entwined our lives are than who I love more. I'm horrible at the idea of loving someone only so much or more or less or all of that.
As for who to spend time with, yes it waxes and wanes. I am trying to watch the waning bit. To the point that if I feel that I 'miss' hubby a bit I tell him and ask for a night of cuddling, massages, movies, or video games. Even the best of us get caught up in NRE and so yeah, the new relationship seems more 'fun'. It's work, but you can keep things balanced.
If you are feeling that you aren't getting enough attention, then you ask for it. Most of the time, if you start questioning if you are still 'primary' it's more about feeling a need or want not being met than anything. That's part of communication. Learning what you are really asking. Often, it's not the question you actually voiced.
As for how do people think of relationships, most have an aversion to using the terms primary and secondary. Feeling it's like a first place and second place thing. We've played with other terms, anchors, entwined, all of that. Really, it's just labels. I use hubby and boyfriend. Those seem to work fine!
Me: Late 30s pansexual poly.
DH: My husband of 19 yrs and father of 3 teen girls.
DC: LDR of +4 year