Yashamaru was Gaara’s uncle and also the brother of Gaara’s mother, Karura. After Karura died giving birth to Gaara (cursed to be the One-Tailed jinchuriki), the Suna leadership ordered Yashamaru to be Gaara’s caretaker—and later, his would-be assassin.
The short answer: He didn't—not truly. But he acted as if he did, and that’s what broke Gaara. why did yashamaru hate gaara
Yet for Gaara, those words became the scar that defined his childhood. Only later did he learn the truth: Yashamaru did care for him, but was broken by duty and loss. Yashamaru was Gaara’s uncle and also the brother