I used to like this guy at school. want to forget about him but i couldn't .how can i get over him?

i may say i am still in love with him.i graduated from school so i cant see him right now but i always think about him. i cant get him out of my mind. my feeings got even stronger now that i dont see him. i think about him every day, hour ,second. i can't do anything i cry alot i am not happy i feel lonly,i can't even have good time with my friends,i don't even eat properly i lost weight b/c of that.the worst part is i dont even know how he felt about me he used to stare at me alot and wanted to talk to me but i was shy so we did not even talked that much but some how i think he has some feelings for me. my best friend told me he sometimes come to her work place to buy things and one time she saw him out side her work place.he was sittin in a car like he was waiting for someone then he just turn his car fast and left when she saw him and she thinks he comes there to see me.but the truth is i dont know what he thinks so tell me how to forget about him please. i cant go on like this