I don`t know how Tess does... «Ship It»

I don`t know how Tess does it. She seems to know exactly what she is, and who she likes, and why. When did she acquire this certainy? And how can I get some of it to rub off on me?
My cheeks flush in the darkness at the phrase rub off, and I shake the visual from earlier that night away.
Because what if... what if I`m not actually queer? What if I come out to everyone I know, but then I realize later that this was just a weird night and after this I never kiss another girl? Then what? Then do I have to re-come out as straight? Take it all back? And who would believe me? Everyone I know already thinks I`m gay just because I ship slash and I like to talk about it. I mean, I could never come back from that.
How are you supposed to know? I mean, really know, like for sure know? Know enough to tell your mom, who will surely freak out and want to bake a cake or something? Know enough to call yourself gay — in public or even in private, even in your own head?
I don`t know. What if I never know? What if I feel like this forever?