Would you be angry?

Last night I asked my girlfriend what we should do tomorrow night ( Saturday night ) and she said I don't know babe anything .. And I said well let's see what we feel like doing when we finish work.
Anyways she just messaged me and said she is now going for dinner with her friends ... And she will come over after ... But that will be like 9pm or something and I already asked her yestedaY what we should do... So I feel like I'm just second option until something better comes up.. 
we are fighting now , and I told her this isn't the first time she has done this .. I have been down and upset and a bit depressed this month due to me having to put my cat down..
She hasn't really been much support really.. 
I'm starting to think .. I'm just not good enough.
She Said I'm fucking selfish cause her work friend is upset .. But yet I am upset to? 
I said she could of invited me .. I know these girls also .. But she still didn't invite me .. What do you think? Would you be angry? If your partner bailed on you?