In my case I realized I was totally in love with both women, and had trouble with the idea of living without either of them. So I guess it turned out I was poly. I wouldnt have known that I was capable of this. Of course as I found out, when you find yourself in that situation and one of the people simply cannot accept you like that, you end up in an extremely difficult pickle.
As someone close to me once said, every relationship is unique and defines itself. Trying to fit it into a box just doesnt work. I could easily see myself not being poly at all with my new love. Not necessarily because I got burned on this, but because no one may ever come alone that we both really want in the relationship. I know we would be somewhat open, but very reserved.