How do I get over my utter devastation at missing my grandfather's birthday three weeks ago?

The whole family was there but me. I missed it due to flight cancellation. I am having a terrible summer because of it. How do I let this go and move on? We don't get to see that part of the family cause they live far away but her birthday is the one time of year we do. Now I have to wait until a wedding sometime next spring. I am devastated. I will see my grandmother and aunt at Christmas but not the rest of the family until next spring. I am beyond devastated and yet I know there is far worse in the world. I had no father and so my Mom's family is all I have. My mother died 6 years ago (I am 31)