The lyrics go, "Forgiving you is easy ... But forgetting seems to take the longest time."
That's the problem with forgiveness. Many people feel they have forgiven the wrong done to them and then when the memories come back they get all angry and upset again and believe that they haven't forgiven.
Let us look at forgiveness more closely.
Forgiveness is an act, not a feeling. You decide, actively, that you will forgive someone who has hurt you. This means you will not seek revenge, retribution, compensation or feel resentment or ill-will towards the person who did you wrong.
Of course, the memories will linger on. The slightest event will bring back the whole situation to your mind and will make you angry or upset once again. This is only natural. Don't worry. Use these moments of remembering again as an opportunity to actively forgive once more. Hand over the person who hurt you to God. Pray for them. You cannot possibly hate someone you pray for. Say to God, "I hand this person to your love and mercy. Forgive them for me!"
What if the person who has hurt you, and never sought your forgiveness, is now dead?
He is no longer your concern. Stop agonising about it. This person is now before God and has seen the situation in all its facets. God will now deal with the situation and that person's role in it. You should pray for that person when the memory of the wrong-doing comes to mind.
What if you need to seek forgiveness from someone who is now dead?
Obviously, it is now too late to seek forgiveness from him. But it is never too late to seek forgiveness from God. Confess your wrong-doing to God and honestly and earnestly ask for His forgiveness. Provided you are sincere and repent God will forgive you.
And once God has forgiven you this is the end of the matter. Stop picking at the situation over and again. Stop feeling guilty at your wrong-doing. God has forgiven you. By picking at the situation you are insulting God in that you are saying He has not forgiven you. That He was wrong that He forgave you.
How do you think He feels about that? Doubting His love, His mercy and His forgiveness.
Accept His forgiveness graciously and move on with a joyful heart.