Black Dragonborn are notorious for their brutal and ruthless behavior. They hear the will of their master and act upon it.
However this Dragonborn was unable to hear the will of his master. Now lost, stumbling blindly through life in madness. He meandered aimlessly, stumbling across a girl from a nearby village.
Their meeting was violent.
And while he was about to end her life, he culminated what humanity he had in him to spare her life. She was the turning point for him to see through darkness. And he loves her dearly for this.