Is there anything that is unforgivable?
I think you are asking if there are certain persons who are unforgivable. We do not forgive situations, but instead we forgive people. Some people are so hurt by grave injustices by others that they cannot, at least for now, even consider forgiving the people who acted unjustly. This is not necessarily the offended people’s last word on the matter because, months or years later, some of them might change their minds. In my experience, I have never seen particular situations that are so grave that no one has forgiven. I have seen some people from the Holocaust of World War II forgive the Nazis. I have seen people forgive the murderers of their children. So, it does not seem to be the case that there are incidents so horrible that no one forgives.
For additional information, see What is Forgiveness?