Ugh, I'm so confused

What do you do when the person that you think you might like just a tinsy winsy bit clearly likes one of your best friends? Ugh, I'm so confused. I don't even know if I like him! I've barely spoken to him, but idk, I keep thinking about him and I'm not sure what's wrong with me.

I've never had a crush on anyone, ever. Even with band members, I don't even really think "oh my god I wish we were in love" although I may say it. I find faults with everyone and in the end I'm just like agsjdjfiabs I couldn't deal with you.

But my friend's so beautiful and I'm just...me. What sort of competition is that? But then, I don't even know if I like him, ugh, I don't know what liking someone feels like. I'm not sure if I just want SOMEONE to like me and he seems like the most likely option, or what.

I started, idk let's say 'liking' him at the beginning of last year, and we sat next to each other in some lesson. We never even spoke when we were sat together, but I just don't know, I felt weird around him, but then I was like "what's wrong with me?". Then he got moved and idk I didn't feel as weird anymore. I didn't think about him for ages afterwards, but then lately I have been again, and I have no idea why. He keeps looking at me, but that's probably because I keep looking at him and he's getting creeped out or something.

He isn't even good-looking, really. Which confuses me because I'm a really shallow person, even though I have no reason to be, I'm not exactly a model, but yeah, this causes me to doubt that I like him too, because I don't like people who aren't like, stunningly attractive. He has good music taste too, and idk, he's funny and oh GOD. I don't know. I get nervous around him and ahajdjsjahshsndncjs I hate it.

Maybe I'm just jealous, maybe I'm jealous because this friend gets everyone fancying her and no one's ever liked me, but I just don't know. And I can't even say "oh, he might not like her" because he's basically admitted it, and his friend's always teasing him about it and stuff. I don't know. I'm just so confused.

How do you know if you like someone?