I'm going to cancel a casual plan at 7:00 after finding out they had separate plans at 8:30.
Did you talk about this with them? Did you talk on doing something later that night?
I sadly didn't know where we would go afterwards.
I'm sorry they betrayed you like this, and you don't have to follow through if they hurt you so much like this. Just be silent and let them do their separate plans, they don't deserve your wonderful company and they're not worth your time.
Maybe we all can plan better next time.
What they did was wrong to you and you didn't make any mistakes. I would be upset too and hope that things work out better for you next time.