I've liked a guy for over 3 years but...?

It was only the first year we got to kind of know each other that really attracted me to him. Now I'm in High School, have no classes with him, and we never talk. No matter how hard I try, I just can't seem to get over him. I usually overthink EVERYTHING, so it's hard to get my mind on anything else when I still believe there's some hope for me. This unrequited love is getting nowhere and it really bugs me that I haven't done anything about it. Any advice love experts...? XD