I have a friend who is not on Facebook, and never has been. One friend. Let's call him Marley, like the puppy (don't spoil the ending, I'm still reading). He didn't leave Facebook. He's never been a member. He knows about it. All of his friends are on Facebook. Marley's wife is on Facebook, and she's my friend there (and in real life). Marley's brother is on Facebook, where he also promotes a band and local tour dates. But Marley flatly refuses to join.