Su Xuan had a reason for telling Mo Chou so much; if it had been someone else, he wouldn't have bothered. But Mo Chou was different; to Su Xuan, she was like an older sister.
So naturally, Su Xuan wanted to help his big sister recognize Lv Rongfeng's hypocritical nature. Even though Su Xuan was also a bit of a playboy, he truly loved whom he loved and wasn't just toying with others. Lv Rongfeng clearly was; he toyed with other people's emotions, which Su Xuan despised most. Simply put, he was a scumbag.
He and Su Xuan were fundamentally different. Su Xuan's flirtations were at least open and typically involved genuine feelings. Lv Rongfeng just deceived inexperienced people into sleeping with him.
Su Xuan really looked down on men like him, especially since he was using Mo Chou's money to support college students, which just seemed even more shameless.
