The people of the Mu Family seemed to be somewhat obsessive; Mu Nan was like this, Mu Ye was too, and she herself seemed to be the same. This obsessiveness was sometimes a good thing, sometimes it became a problem.
But regardless, Mu Cheng was completely enchanted by Fourth Miss Zhao, to the point of losing his mind. Whatever she said, he would not believe it; even if she forcefully made him sever ties with Fourth Miss Zhao, he feared he would not be content in his heart, and it might even turn into his personal torment.
Forget it, let's just find an opportunity for him to see the true face of Fourth Miss Zhao; only then will he completely give up. The worst-case scenario would be to keep a closer watch on him, to prevent him from sinking deep into the mire like in his previous life, only to have a sudden realization at the very last moment, and thus endure a lifetime of scorn from his own people.