Do you have to be in a relationship?

I’m in high school and I don’t have a boyfriend. Most kids think this is weird and take the mick out of me for it. Some have even gone to the point of assuming I’m gay, which with all due respect I’m not.
They think this because I hang out with a girl who is. I really like her and have lots of gay friends.
The thing is I’m tired of it. Do you really have to be in a relationship in school? I just don’t take an interest in boys that way and I’ve tried explaining that to certain people but it just falls on deaf ears. Why is it that if you’re not in a relationship, people think you are strange or unusual? Is me not having a boyfriend at the age of 16 abnormal?