The only person to suffer from un-forgiveness is ourselves. Others can't experience what we think and feel, others can't read our thoughts, only we can get to grips with them.
Our pain, torment, self mind talk is purely ours and we are thus the only ones privvy to this, if we get upset then we get upset, no one else will. If we are to move on in life then we must forgive no matter how hard that is.
Keeping malicious thoughts and feelings alive as some kind of validation is evil and un Godly and negative and makes you a worthless person in society. Un-forgiveness is like drinking poison and expecting others to die, it will never happen.
Many people hide behind unforgiveness as a facade to their own failure, they become bores with endless versions of "their story" the long, short and abridged versions to tell unsuspecting listeners.
Some religions breed unforgiveness as a respectable vendetta to a life of failure and incompetence and substandard living and subliminal devil worship.
If you have love within you you can forgive, if you don't then you know the score....