Meng Li's motives for getting close to Shang Zhuo were never pure.
At first, she wanted a gun. Later, she wanted to fight back against her stepfather, who was eyeing her with ill intent, and to take advantage of Shang Zhuo's resources...
But she didn't know that Shang Zhuo had long seen through all her disguises. He was willing to be used because he'd fallen for her.
Later, when her conscience finally pricked her and she tried to come clean, he smiled and said, "Keep lying. I never said you had to stop."