Think of a person who hurt your friend to such extent that he had to move away in order to save himself – anger would be a natural reaction towards the person who pushed him to such a decision.
But instead of dwelling on that anger consider what led him to do such a terrible thing.
Consider who he is as a person – disposition, quirks, motivations, etc.
And realize that despite the terrible things he has done, inside is a lonely and hurting boy desperate for affection and acceptance.
I think I’m beginning to understand what kindness is. It is giving somebody a mug of hot chocolate after a tiring day. It is being considerate of what somebody else is going through. It is offering to carry another person’s heavy load to give them relief, even if only temporary. It is going the extra mile in doing something for someone.
Kindness is… seeing the lonely and hurting boy beyond his nasty actions and treating him opposite to what he deserves.
Anger and ostracism will not make him realize his wrong – it will only push him more into isolation and defensive actions – but kindness will.