Xu Ming watched everything and hesitated. He wondered if he should stop it. He realized how hurtful it could be when someone you liked was killed. The man that was lying on the ground must have a family as well.
Xu Ming didn't want to see someone die right before his eyes, but he had a decision to make.
It was a conflict of choice that he was facing. If he didn't stop the guy from killing that man, he would be a part of the evil as well. But if he stopped him, his own life would be in danger. He realized that the man in front of him was way stronger than Xiang Feng. He didn't have the strength to do anything.
And even if he managed to protect the man by offending his fellow Disciple, he would be left behind. There was no way that the disciple would bring Xu Ming to the sect after that. He would not be able to go back and that was something that held the highest importance for him as his necklace was inside the sect.