Christian forgiveness isn’t a matter of forgetting that someone has wronged you, or pretending the offense doesn’t exist. It’s a matter of releasing the debt (like the king in the parable of the servants) and turning it over to God. Then he can decide whether to charge it to them or to Jesus. At any rate, the debt is no longer owed to you.
For this reason, reflecting on the greatness of our own sin can really help in the fight to forgive others. When we think about the infinite debt God transferred off of us, it becomes a little easier to transfer a (relatively) small debt off of someone else.