Fantasy series that ends with deadly swordsman being sent back to save family

[Susan]

The high fantasy series follows a dark hero who hunted and killed the bandits who killed his wife and son just as he was returning being a soldier. He becomes known as an implacable killing machine who ends up saving the world. His final act to preserve mysterious and powerful ones causes a fatal poisoning. They reward him by sending him back in time to his home just before the bandits arrive. He saves his wife and child and dies before he himself comes home, closing the loop that made him what he was.