This one is slippery.
Forgiveness cannot be contingent upon an apology. You do not accept a man's apology as restitution for his sin against you. That's too cheap for grace. You don't allow him to make it up to you. That also is too cheap for grace. To forgive is to accept the consequences of another man's sin as against you as your own instead of requiring that he do the one thing he cannot: pay you back. He can no more make it right than you can be made whole again by taking vengeance. Something has been broken. All you can do is freely give what has already been taken from you. If he takes your coat, then forgiveness is considering it lost.
The only way one can afford to take such a personal loss as sin will demand is if he has access to the riches of Christ. Then, whether it was reputation, power, freedom, security, or intimacy that was stolen by the sin, you can freely let go the debt because yours is an inexhaustible storehouse of wealth in Christ.
If he does change after you've forgiven him, it will not be in payment to you against the debt he has incurred. It will be in response to the payment in full you have already accepted on his behalf. This grace will change your life and his as you both experience the mind of Christ.