Why cant i let go and move on and get ver my ex ?

my ex broke my heart by dumping me over facebook for his current girlfriend . i cant get him off my mind , it feels like my life is on pause. i keep feeling like what if i never txted him saying it was a good idea to have a break for the summer ( when really i was txting him for the break because i knew he was cheating) . i don't want him back i just want him to out of my heart . id rather like to go back to college in september and show him that i have moved on from him rather then looking over my shoulder . i really loved him ,what can i do