How do i move on?? its very hard for me...?

hey there..!! i really love a girl and was in a relationship with her... but things happened between us and she moved on... she is now committed to some other guy... i really love her a lot and have told her many times... she says she cares fr me.. but just as a friend and she considers me as her best friend.. but its HARD FOR ME TO MOVE ON... I REALLY WANT HER IN MY LIFE BUT SHE SAYS SHE CANT GIVE ME A SECOND CHANCE.. ARGHHHH its very irritating... what should i do?