Hey there Emma!
I 100% understand where you're coming from. I've felt the same way before, and sometimes even still do! All I can say is that it honestly doesn't matter as much as you think it does now. I'm a senior too, and have had two relationships in the past three years. I entered them both because I liked the two individuals, but also because it just felt like something I should do in high school, if you know what I mean. You seem to feel this way, wondering why your crushes don't become real relationships, and I think that society and pop culture has just given us the impression that we're supposed to have some sort of romantic experience before we even go to university! And to be honest, if I could go back in time, I would have chosen not to enter those relationships and would have decided to spend more time on my friends instead! Trying to balance school and a relationship is often hard enough, but balancing them with friends is even tougher, and no matter how you organise it, you'll end up sacrificing something. High school relationships often don't last, not because people don't really like/love each other, but because we don't know enough about the world yet to decide on what we want. And is there much point in investing so much of your precious teenage life (the rare, scarce amount of time you have before adulthood pushes immense amounts of responsibility onto you) onto a relationship that most likely won't work out?
This is not to say at all that I am discouraging you from relationships completely. I'm just saying that if you feel that having a boyfriend is something you should have rather than something you want, you don't need a relationship in your life. Lots of people don't have a boyfriend until they're in their twenties, so what you're experiencing is definitely completely normal!
Hope this helped (sorry that it came off a little rambly), and feel free to
PM me if you ever need to talk!
Kyra