Friends?

There are friends that stay forever and others that go away. In your life you meet different people. But when do you know if that "friend" is actually your friend. You never know who to trust. You basically have to risk yourself to make friends and try to trust them. Every relationship is based on trust, so friends should be based on trust too. Sometimes you click fast with a person so you two automatically become friends. Other times it takes a while for two people to be friends. It all depends on the two people.
Best friends are classified as two people who share a special bond. People who share everything about themselves. But what happens when the other person makes a mistake? What if during the friendship one person decides the other is changing, but there really not. Doesn't that mean that you don't know each other well enough.
You know when your friends with someone when you don't argue about things and just talk things out. Sure you might have a couple of close friends but only one true best friend.

Question to ponder:
how do you know which friend is true?