Why should bones curse white?

Hua turns into a demon god, creating the illusion that human beings are devastated, and letting Bai kill himself when he chooses the world or himself. White wants to kill himself and die with her. But Hua finally swore an oath (Oracle): "Bai, I curse you in the name of God, forever, never old or dead, never hurt or die."

Because Bones wanted Bai to live, he was cursed.