This article is from the Polyamory FAQ, by email@example.com (H. Wilper) with numerous contributions by others.
I'm not sure; only you will know, and according to the philosophy
of some folks, people aren't polyamorous, although behavior can
be. Some people find that approach useful, and others prefer to
think of "polyamorous people".
Some polyfolk tend to recognize themselves in the descriptions,
and can only be restrained with difficulty from jumping up and
down and screeching, "See! See! I *knew* it wasn't just me!
Hooray!" If you aren't sure you're poly, the best practice is
probably to act kindly and responsibly, and to communicate
clearly to the best of your ability as you learn; come to think
of it, that's the best practice for polyfolk, too, so you'll be
one of the crowd anyhow. Besides, being polyamorous is not
inherently "better" than being monogamous, so there's no need to
feel like you have to pledge allegiance or anything like that
just to hang out and look at the questions.
Another thing to consider is that the word "polyamorous" is, like
all labels, just a tool. What you do and how you treat the
people you love is probably more important to them, in the long
run, than whether you fit a particular descriptive term, so don't
sweat it, okay? And take good care of each other.
An alternate point of view:
"There aren't polyamorous and monogamous people; there are
polyamorous and monogamous relationships. The same person may
at various times be happy in both monogamous and polyamorous
relationships at various times in his/her life. What is right
depends on you and your feelings, and the feelings of those
you are involved in relationships with. You may at some times
be involved in a relationship that is monogamous, and that
may be the right thing for the people in that relationship;
at other times, you may be in a relationship which works
better as part of a polyamorous network of relationships. In
any case, the important thing is probably to act kindly and
responsibly, and to communicate clearly with intimate
partners and potential partners about these issues. Don't
deny your feelings or the feelings of those that you care
about. Get in touch with how you and those you care about
really feel, rather than how society wants you to feel, or
how you think it would be logical to feel, or how you've been
told polyamorous people (or monogamous people) should
feel. Then behave in ways which are honest, and which make
you, and the people you care about, and the people they care
about, happy and fulfilled. If this results in you having
more than one intimate relationship at the same time, or
being involved in a relationship with more than two people,
those who are big on categorizing and labeling people will
label you a 'poly person'."