It is, when the act of forgiveness does not allow the person to move forward in life in a healthy manner.
You are using an example of a situation that does not implys a degradation of ones life and relations.
Have you ever felt anxiety?
Have you ever felt anxiety, every day, in an extend of 3 years, constantly, non stop, all the time? Do you know the repercussions of it on a daily basis? People tend to isolate, they do not want to be around other people, everything triggers them, they also don't want to be a burden to others.
Everything exists on a spectrum, and not everyone react the same way in different situations.