Regarding the betrayal by Speedy Slash and Ke Zhan, Xin Yun seemed unfazed on the surface, but in reality, his heart was always blocked with panic. Such incidents, no matter how many times one experiences them, could never become a routine. Quite the opposite, each additional betrayal added a layer of depression to his heart.
Although Ke Zhan and Speedy Slash had not actively betrayed him, it was only a matter of time. Xin Yun didn't want to give them a chance. To prevent betrayal, one option was to kill them, and the other was to sever their relationship before any betrayal could take place. Xin Yun chose the latter.
Of course, Xin Yun had considered killing these two, but they had only grown indifferent, not traitorous. If things dragged on, he didn't know how long it would take for them to betray him, if ever. They might just be dragged along for a lifetime, which was clearly not what Xin Yun wanted. Once their hearts were scattered, what was the point of keeping them around?