Although Lu Bei didn't say it outright, his actions showed Zhu Xiushi that Bai Jin held a high position in his heart. Speak out of turn, and receive a punch to the chest.
The last beauty who received a punch to the chest from Lu Bei was Ji Chen. Zhu Xiushi was on the scene, and witnessed it firsthand, and didn't doubt his ability to act.
Feeling sad, we've all been together through life and death, fought against Qiyan, and teased the Grand Tutor together. Now that Lu Bei is elevated, able to go to Xuanlong and kill the demon king, we can't play together anymore, and he'd fall out with her without hesitation over a woman.
Thinking of this, she wept in the corner.
"Stop the act, my senior sister doesn't fall for such tactics."