It may seem that your unwillingness to forgive a wrong is hurting the recipient of your anger, but that is not the case. That person is not experiencing higher blood pressure, and diminished ability to deal with others in a positive manner. You, as the angry person have these symptoms. The other person may wish for resolution, but that is not nearly as bad as carrying a grudge and feeding your anger. Basically when you are angry at a person you give them a route to cause you continued harm.
Anger is a secondary emotion.
It can be a reaction to other emotions such as fear, hurt, insecurity, and other painful emotions. If a person latches on to the reactive emotion rather than the primary emotion, there is no way to deal with the primary emotion. The person does not deal with emotional issues, and stagnates. It is obvious that anger is a rather negative way to spend your life, so what can you do to prevent these angry feelings. It is not a good idea to hit a pillow or kick a bag, or find another way to vent the anger.