Time after time, I hear people say, "I just refuse to forgive them!"
Yet, I know what holding onto that anger at a cellular level does to the body. The one holding on is the one who suffers the most.
Anger eats away at the body, at the energy system, at the organs - it is an emotional cancer that will literally eat away at your body.
In fact, Louise Hay has said in her book "Heal Your Body" that cancer usually develops from deep hurt and long standing resentment.
Every situation is different and the levels of hurt, betrayal, fear, etc varies with each individual. You must find what is comfortable for you and your unique situation.
This article by Sara Staggs from Psych Central is a short but good one. Make sure you read the comments and Sara's answer as she explains more.
Should You Forgive Someone Who Harmed You? | After Trauma