I'm pissed at my friend for not inviting me to a party
Why didn't he invite you to the party?
He did this for petty reasons because he wanted to hang out with the girls
I understand how betrayed you must feel by your friend. Friends aren't supposed to exclude you from parties. That probably means they really aren't your friend.
That's ridiculous. Of course we're friends.
I don't know, it seems like your friend had a petty reason for excluding you. Someone who is your friend wouldn't exclude you from an event just so that they could talk to girls. It may be time for you to reevaluate this friendship.