Anyone got any idea's that would help me get over my ex ?

my ex and i where going out for five months and then out of the blue my friend txted me and told me he saw my boyfriend at the time holding hands with another girl . so i txted him and told him i wanted a break for the summer and he said ok i love you and then a week later he chang's his status to say that hes with the new girl on facebook so basically i got dumped over facebook. when i had to txted him for the break i was so upset txting him that , that i felt like cutting myself ( but thankfully i didn't) i felt so sick for weeks after the break up. I thought for weeks and i still feel like i failed and that i didn't no how to fight for him but then i realized that i have to let him go , i no i love him but there's only so much heart ache i can take and it feels like i have no heart . i find it hard to connect with other guys ( we broke up in april and its now june) one guy asked me out on a date but even the thought of it made me feel guilty . i think about him constantly and dream about him when in my heart i no that i have ta let him go , he doesn't love me i get that , so why is it so hard for me to get over my ex ?