I'm a girl, and I can't tell whether I'm bisexual or gay. I like girls a little more than boys, but I don't really know.
How do I know what my sexual orientation is?
I would ask you, "do you feel like you need to come up with a label?" Is there something about identifying as one or the other that would be helpful for you? From what current science has told us about sexual orientation, it's a spectrum. There are people on the spectrum who are clearly gay, or clearly heterosexual, and then there is everyone in between, which includes being "bisexual" (which I guess in the spectrum would be smack in the middle?)It may be too early for you to identify as any one thing on that spectrum (as you say, "but I don't really know"), or maybe as you move through life you just won't identify as any one thing, and that's totally okay. The most important thing, in my professional opinion, is to accept yourself, fully, for whatever it is that you are. The second most important thing, in my professional opinion too, is to be honest with yourself and your partners about however you do identify your sexual orientation.