Luhan was in love with a pop star from a group called EXO with 11 mambers. 

From all the 11 mambers Luhan fell in love with Oh Sehun. 

Oh Sehun and Luhan go to the same school and they even have the same classes together. 

But Sehun didn't even notice Luhan untill the competition to get into the 12th spot and become an EXO mamber.