Looking at things, I've always been a more descriptive than prescriptive girl. Prescriptive is typically knowing what types of relationships you want and then looking to fill that role. While descriptive is just describing what types of relationships you happen to have right now.
I'm married, we just hit our 18th anniversary. We ventured into poly about five years ago and like most relationships, still working on it. A lot of married couples going into poly get a bad rap. They are only interested in unicorn hunting or are putting restrictions on what other relationships could be and that gets looked down on. While we've never been unicorn hunters, and many single poly people also put restrictions up, it seems, to me anyway, that married couples get that reputation before they even open their mouths.
Now for us, we don't use the terms primary or secondary often. The few times we have discussed it has been when DC has mentioned he's not really for that kind of relationship. He wants to get settled into his own life and career before being a husband or father or being that fully responsible to and for someone. Or when hubby and I discuss it often it's to discuss that we both understand that feelings have nothing to do with it. I don't love either one more or less, though the relationships are in different places.
There's more established with hubby, we talk about how if something more serious were coming, like DC living with us or that kind of thing, it's farther down the road, like years. That's not out of a sense of hiearchy, more just that I am not comfortable with that for a while. (When I'm thinking out of NRE state!)
For us, at least, the terms secondary and tertiary are about where the relationship is now, not what the relationship will always be or is allowed to be. Hubby has actually gotten pretty comfortable these days about the fact that I feel for them both in the same amount. Even going as far as asking me if I've sent the same pics or cards to DC, or while we were out today for hubby's bday and v-day, if I was sending something to DC or had picked him out anything yet. Because the love isn't limited, just time and visits and mostly that because of it being long distance still.