How do you get over a guy you have a crush on?

i been likin this guy for like forever months to be exact and then i found out he has a gf. i know his gf cuz were related. yea i know it sucks! then one day i admitted to him that i did like him but am over him. somehow someone told him and he asked me. yup cant rely on anyone. then i been trying to get over him. like new people but he wont get out of my head! it feels weird seein him and knowin he knows i liked him like that. we were good friends before all of this. what can i do to get over him?!