unforgiving
adj.
unwilling or unable to forgive or show mercy
a surly unforgiving old woman
adj.
not to be placated or appeased or moved by entreaty
grim determination|grim necessity|Russia's final hour, it seemed, approached with inexorable certainty|relentless persecution|the stern demands of parenthood
Synonym: grim, inexorable, relentless, stern, unappeasable, unrelenting
Antonym: forgiving