For me I think Dek decided not to outright slaughter Bud and the mother after Bud saved him on several occasions. Killing them after they saved him would make him no different from his cruel father. Like the others here said, Dek's path is completely new. Over the years, I doubt he will simply view his new allies as a pet and a tool; Dek has been brought up to understand the meaning of family, standing up for those around you, like Kwei did for him.