Forgiveness is Optional

You do not have to forgive someone even if they apologized. This is absolutely normal. You should not feel guilty about this and forgive due to these feelings or out of pity for the person. Their actions hurt you, and you have the right to accept the apology or not. An important point: you should not manipulate with your resentment by staying in the relationship with the person. Usually, communication is minimized in such a situation (if you need time to think over the situation) or ceases altogether.