I have an empty feeling whenever i look at my old gf PLZ HELP READ DEATAILS?

I am 12 years old, and in grade 7. My old gf, is in my cl, and we sorta chat sometimes. She was everything to me and I loved her a lot. But I was shy and weird so she dumped me everytime I look at her I just feel like huging her when she is talking to her friends from the back and saying "I love you". But she is into other guys.. what should ido to forget it plz help