Wow, that's low. Are te sure they're really best friend quality? They could be doing it for many reasons... Maybe they feel insecure. Maybe they have a crush on him. Maybe they want to look cool. o they could just not know what the problem with that is.
Your friend is a backstabber. Why would a friend mostra embarrassing video of te to your old boyfriend? She is betraying te and te should not be Friends with this girl. te can get better Friends than her.