Forgive, not for the betrayer (he/she could care less), but for yourself.
Move on without the burdens of negativity.
Treat the forgiven with detachment. As far as you're concerned, he/she are just another person in the elevator.
Let life do what it does best: It always gives each person what they deserved.
And for Buddha's sake, learn the lesson.
NEVER forget it (lest you will be presented with it again).
Namaste, JaiChai
RE: Of moving on and forgiveness