I break off the friendship and walk away. I am a firm believer that what comes around, goes around. Their actions will come back to bite them. Especially when no one will ever trust them.
All are teachers and students.
Learn the lesson, move on.
my advice is for you to stop being there friend you can't continue being that person's friend i believe in karma and karma is going to bite them in the butt
If like me, you have no friends, there is no risk of betrayal. :)