Sorry you are feeling abandoned! I can understand why you are hurt.

How old are you if you don't mind sharing? Friendships come and go - especially when we are younger, I think. However, an abrupt end to a friendship is confusing and hurts. Did you ask your friend why she wanted to not speak with you anymore? She may not answer, which you can't control - but I think it is OK to ask. Were you friends for a long time? Any recent arguments?

Regarding your other friend - were you able to wish them a happy bday? Perhaps they thought you had received an invite to the party but it feel through the cracks somehow?