When you decide to love someone, even if its just a friend, you give part of yourself away to them. When they are with you, you don't notice, but when they leave your life, the part of you that was given leaves too. You are left feeling incomplete and have a void in your heart. It's extremely hard when you don't expect to loose them. But even if you know you will lose them and are "prepared", the pain of loss still hurts. A lot of times we don't understand what it means that they are gone. It is so hard to imagine life without them. We expect the loss of their friendship to hurt less. How wrong we tend to be.