The past does not change when we choose to "forgive" someone.
The hurtful behavior someone once engaged in-- they still did it.
The mistakes we made-- we still made them.
The misunderstandings that occurred-- they still occurred.
The damage that was inflicted remains.
Forgiveness is not about changing the past.
It's about giving ourselves permission to shift our focus in the present and future when we think about someone.
It's about deciding that what happened in the past-- while perhaps still important-- is not going to be the only, or the defining, aspect of our present and future relationship with a person.
When we forgive, we're not saying what happened in the past is "okay."
What we're saying is, "I am open to a future with this person that is not solely defined by the past."