Ma Nanji would stand on a completely different side from Musheng, but it was only because as a child, he was too bewitched by Wen Xuanming and idolized for his good looks from a young age, which spoiled him a bit and made him arrogant. He had grown accustomed to being self-centered.
Day after day of brainwashing might have led him to view Wen Xuanming's affair differently, but deep down, he wasn't a bad person. Otherwise, he wouldn't have grown to feel more and more guilt toward Musheng. Despite years of brainwashing, Wen Xuanming hadn't managed to erase that thread of doubt in his son.
Especially today, having been enlightened by a few words from Musheng, Ma Nanji realized he owed his mother even more. She worked hard outside, humbly earning that supervisor's salary, all to provide him with a comfortable life. He had accepted some small favors from Wen Xuanming and completely forgotten about the enormous injustice Ma Changying had to bear because of the divorce.