I said no to the only girl that liked me and it eats at me everyday

I was in grade 10 at the time. She actually liked me, despite me not being the best looking guy, short, all of the above and yet I told myself I wasnt ready for a relationship, that i wanted to "focus on school". Every day I think about her, I still follow her on social media and more, she even took the first step. She wasnt the best looking woman or anything but goddamit look at me. What have I fucking done, it hurts so much. First year in university I finally gained enough confidence to go message her again, just maybe, just maybe she wouldnt think Im some over confident asshole, because yes I think i love her now. Well, I was then told, actually not by her but my friend that she had a boyfriend. I just wish I could tell her how sorry I am. I am so sorry I said no, I was such a asshole. I know I should get over it but I just can't stop thinking about how I probably hurt her. In my 17 years of life she was the only one. Maybe shell read this, im just so sorry, I hope you have a good life, I understand it wont be with me.