Not getting mad when there is just reason to (righteous anger) is sensory deprivation and causes you harm. It is neglect of SELF (feeling guilty about this would be just).
Get mad ABOUT A SITUATION or simply upset, don't let people make you feel self-conscious about getting mad/upset and feel guilty that you are being mean (getting mad AT A PERSON).
It is unecessary to forgive someone unless YOU (ONLY "you") decide it's necessary (if you don't first hold the other person in contempt, there is no reason for them to need forgiveness), other people try to elicit your guilt and subordination, but if you have been wronged INTENTIONALLY (not careless or mistake), you have been wronged.
They will also try to convince you that you need forgiveness for doing something intentionally, make sure it is righteous anger so that you will always have peace in your mind and conscience.