How do you get over disappointment- esp when you had high hopes?

i was going to get a chance to see my ex again. we had many differences in the past, resulted in a year of not speaking, but recently i apologized, we put that aside and decided to move on with life- of course without each other, bcos maybe its for the better. then i received an invite to a gathering that she was going to be at, by a mutual friend. i was so excited that i was going to get to see her again. no matter what i know i still love the girl and that its only bcos of circumstances that i have to let her go. but then i heard she may most prob not be attending the party bcos of a competition she has overseas. it hurt alot to hear bcos i was hoping really badly to see her. i may never get the chance again. how do you get over disappointment like this?