Please help!

I went out with this girl from school, then we broke up but we've remained close friends ever since, but she's year 11 and i'm year 10, so she's leaving in may but i'm still in love with her even though she has a new boyfriend, so i wanted to know any tactics i could use to stop being in love with her. BUT also i really want to know to to say good bye when she,leaves! PLEASE HELP!