I'm upset at my girlfriend for leaving me alone at her house
Did you not want to be alone or what?
No, I always want her near me no matter what.
Sometimes they have other things to do. You cannot expect them to be with you all of the time.
You don't know us or our relationship.
It is odd to expect someone to be with you all of the time. This is not a realistic expectation to have of other people in your life.