Letting go and forgiveness has nothing to do with thinking of them in a positive way. Remember some people forgave Hitler. That clearly did not mean that they liked him, who would? They did it for themselves, because they recognized, that harbouring hate and anger toward another person however despicable they be, only served to poison their own mind, their own soul. Therefore the act of forgiving was done for their sake, not for the other persons sake, You may never see that person again, you may not like that person, it does not matter. The purpose of forgiveness is about releasing your own resentment and anger, so that you no longer allow the memory of that person or their actions continue to rob you of your inner peace, happiness and success in life.