As humans the issue of forgiveness can be a really difficult one that the flesh often struggle to deal with. In the case like you just mentioned, the thing is to constantly pray to the Holy Spirit to remove and form of unforgiveness in our heart and do our part in praying for the individual. The more we do that, the more the hurt in our seem to diminish.
Sometimes we don't forget, but as long as you've forgiven from the heart it's all good. Overtime the hurt will fade away. We should also pray that love should fill our heart, that we should have the heart of Christ. The more our heart gets filled with perfect love, the more hurt and pain fades away. Perfect love casted out all impurities. This thing sometimes requires conscious efforts.