I'm mad at my girlfriend's guy 'friend'
Why are you mad at your girlfriend's guy friend?
Because he left the party early when he was supposed to help her move
He might have had a good reason leave the party early. It's not going to look good to your girlfriend if you are upset at her friends. If she isn't mad you shouldn't worry about it.
Sorry, It just bothers me.
If your girlfriend is not upset about him being not able to help her move,  you have no reason to get bothered about it. Probably you should help her move.