The true meaning of friendship is when you consider the other person's well-being to be as valuable as your own.  If you feel this way about a person, you are truly their friend.

If you consider that another person's good is as important as your own, you will treat them the way friends are supposed to treat each other.  You will make sacrifices for them when, by doing so, you can help them.  You will make sure that you are behaving in ways that will not hurt them.  This is the essence of friendship.

If you are not friends with someone, you may care about their happiness, but not as much as you care about your own.  But if you are true friends, you will care as much for the other as you do for yourself.