How should a friend be?
[ BE WHO YOU ARE & SAY WHAT YOU FEEL CUZ' THE ONES WHO MIND DONT MATTER & THE ONES WHO MATTER DONT MIND ]
If your best friend excludes you you should act like it does not bother you. After that you should just hang out with another friend. Later on your friend will come back. If that does not work you should call and ask your friend to meet you somewhere so you can talk to them about why he/she excluded you