Not so sure

I saw someone in my family doing a sin, nothing that would land jailtime, but I saw them do it no less. They don't know that I know and now I'm lost. Worse than that this person hurt me a lot in the past and for the most part I forgave them, but I'm getting to the point that I don't know that I can. I'm feeling convicted to because God has forgave me countless times and this is not even against me. Why is it so hard for people to forgive? I think it's almost like saying even though you hurt me deeply I'm going to allow you to be a part of my life. I think Christ endured much more than physical pain on the cross. When you see someone you love doing something destructive it hurts a lot just imagine that intensified infinitely since it is every single person who has hurt Him in many different ways.