Tu Su originally thought that he and Ouyang Shaogong would never meet again after the Penglai War.
But he didn't want things to change forever, and when Penglai saw him again, he couldn't leave that person alone.
He brought him back to the human world, sheltered him from wind and rain, and just wanted him to live in peace for the rest of his life.
But in the end it was just wishful thinking. Ouyang Shaogong will always be Ouyang Shaogong.
Destiny, how wonderful and absurd...