I'm upset that my girlfriend got to go to a concert
What are you upset about?
I am upset because I can't go with her.
It is okay to get upset about small things.  But, It isn't your girlfriend's fault you can't go.
I just want her to let me go to this concert with her.
Next time pay for yourself and go by yourself. There is nothing weird seeing your gf who didn't want you to go at a concert.