In our relationship, there IS a primary and secondary role, I am married to a man, then we have a girlfriend, so she is currently secondary, since we have not been with her long and are still entangling ourselves with her.
However, we don’t use those terms in conversation. We know her as our girlfriend, as things grow and progress we would say “lover”. We don’t even use those terms with one another, we simply realize that we will more than likely never fall in love with anyone as much as we have with one another, though we do believe we can and will fall in love with another woman, if that makes sense?
Then again we aren’t going huge with how many relationships we have, so maybe in larger poly groups those terms are easier to use and easier to make connections between the people.