Have you ever forgiven someone for an offense and then days, months or years later, the feelings of hurt or anger return? We think, "I know I forgave that person, so why do the feelings keep coming up?"
Forgiveness that doesn't seem to last (and I say seem to, because forgiveness is an act of the will first, not a feeling. The presence of emotion doesn't equal unforgiveness) is often because you haven't fully processed your hurt and secured your identity in God...you don't believe that He can give back what was stolen from you. The following addresses the first part of that statement.
As Christians we often feel like we need to act super holy and, therefore, can't say what we really feel. But those feelings and thoughts are real and they're really in you. And God knows all of that is in there, anyway. If we aren't free to express and work through our feelings of pain, and even anger, then they will fester and turn to bitterness. Eventually hurt turns to anger because anger is less vulnerable. It feels more powerful. If it goes on long enough I think many of us become adept at bypassing hurt feelings altogether, and go straight to the anger response.
But, think about the things David said throughout the Psalms - the ills he wished on his enemies. We know him to be a man of honor, in that he didn't kill King Saul when he had the chance, though Saul was intent on killing David. Perhaps it was because David had already vented his anger, fear and hurt to God, that he was then able to walk in righteousness toward his enemy.
I think it was Kris Vallotton that gave the example that if someone runs over your foot with a car and you forgive them, the pain in your foot doesn't go away. It's the same way with pain in our soul.
I've known people that experienced very painful things and were NEVER allowed to speak of them. Families chose to behave as if nothing had ever happened. What do you imagine that does to a person's heart and identity?
I think if we could give each other grace to say things that may not sound very "Christian," just long enough to get it out of our systems, then we could possibly find wholeness and restoration could come much quicker. Even if the broken relationship itself is never restored, we are free in our souls. These things don't need to be said to the offender, but to God, for sure, and possibly to a trusted friend or professional counselor.
We are still living this spirit-led life in our humanity. I believe that God is pleased with us when we choose to forgive, despite our feelings, and then continue to move in the direction of healing and wholeness and Christ-likeness.
Sweeping things under the rug only leads to a lumpy rug. That stuff doesn't just go away.