The world doesn't change in front of your eyes, it changes behind your back.
It goes without saying that your friends are usually the first to discuss your personal business behind your back.
Whoever gossips to you will gossip about you.
If people talk behind your back, it's because you're ahead of them.
A friend is a person who goes around saying nice things about you behind your back.
People who serve you without love get even behind your back.