I too entered poly as a single person. I met my now poly boyfriend of 3 years at a party and he said he wasn't particularly looking for anything but was open to see what developed if I was able to accept that he had a Long distant girlfriend and that was not going to change, and if I wanted to explore anything with him it would be mutually nonexclusive. we have been together for 3 years, he now has 3 girlfriends, I am the local one, and I have a long distance sweetie, in my long distance relationship I am a secondary. In my local relationship I am neither primary or secondary, it don't fit in any mold I have read about so far.
I find myself always translating words in the poly literature when they don't quite fit my situation. I think we need to write some new books to fit the myriad of different possibilities. Please know that you are not alone and there are many solo or single poly folk around, whether by choice or circumstances and we have every right to still call ourselves poly, whether we are in multiple relationships or none.