Why can't I be in a relationship?

I'm 19 and never been in a relationship, i would like to have a boyfriend, but whenever i like someone i don't tell anyone and just ignore that person and don't even try to talk to them but i stalk their social media and make fake scenarios about them all day until i just move on. I have never even had a talking stage or situationship, my interactions with males are so limited, also no one has ever showed romantic interest in me (except for like 3 times in summer camp during middle school) and lately it started messing up with my self esteem, i always considered myself quite pretty and a funny person, but now i started doubting it, but i also see a lot of girls who are just like me in happy relationship, so i'm just confused about what is wrong with me, why am i never approached by anyone and why can't i approach guys i like

Why can't I be in a relationship?
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