The Last Bucelarii (Book 1): Blade of the Destroyer by Andy Peloquin

The Hunter of Voramis is the perfect assassin:

Ruthless, Unrelenting, Immortal.

Yet he is haunted by lost memories, bonded to a cursed dagger that feeds him power yet denies him peace of mind. Within him rages an unquenchable need for blood and death. When he accepts a contract to avenge the stolen innocence of a girl, the Hunter becomes the prey. The death of a seemingly random target sends him hurtling toward destruction, yet could his path also lead to the truth of his buried past?