For myself, I have no idea.
I have been aware that I can love more than one person in a romantic way for a very long time...
I have been the classic serial monogamist, dumping one boy for another just so I could explore the other in a "right" way. I hurt a lot of people due to this.
When I was in high school I cheated on my first love with his best friend. That is probably the closest to poly I ever got when I was younger... I remember thinking how they were so different and each provided me with something unique. I had no idea that polyamory existed and broke it off with both of them in an attempt to make things right. It was a package deal to me, all or none.
The situation with my ex husband is a bad example for some reasons (abusive relationship) and good for others (attraction stifled and sex drive plummeted). Being monogamous with him for 8 years killed my sex drive. It is possible that it was all him being a shit hole... but I'll never know.
That relationship is why I question almost everything about my love life. It completely fucked with my head. Who knows if I can be mono because I never had a good shot at it.
When I met O, I was "dating" another man, T, long distance. T wanted to become exclusive with me (long distance?!) and that seemed impossible to me. The relationship with T turned into friendship and some heartbreak late last year.
J is the current other. Sometimes I wish that I could just be a swinger. My head and body don't really work like that, however. It feels like feelings complicate things. Now I have to consider him and his feelings, mine, and O's.
Then there is the casual sex... both with friends, (the best!) and boys I labeled as boyfriends for the week we "dated" for society's sake. Didn't want to be a "slut"!
Oh yah - then there was that foray into "lesbianism" last week. haha.
.....but - Who fucking knows how to tell if you are poly/mono, etc. I bet someone else could easily label me based on the above stories, but I cannot even do that for myself.
My sexuality seems to be, well, situational. Is that a title? "Conditional bi/mono/poly/swinger" huh.