I want to know how can I forget somebody who hurt you?

I met this guy in my new job, I was so excited for this new job and this guy was so nice to me all the time and i started like him i accepted to go out wih him and we kissed at the third date but then he changed his attitud and showed me not interested on me but at the same time he told my friend I dont care about him and I' m so upset that he's putting like that as my fault and i feel so hurt for him