Even though the Celestial Venerable Qilin really wanted to kill Yun Hao to avenge his beloved woman, he was still worried that he might not be a match for Yun Hao, who possessed a pure golden Primordial Spirit. He also feared that even if he managed to kill Yun Hao, he might be killed by the people sent from the Upper Realm before he could even bury Ah Li!
So, at this moment, his only choice was to temporarily ally with Yun Hao, waiting to fight the people who came to intercept them before reconvening for another battle!
The reason for choosing to ally with Yun Hao was partly due to Yun Hao's strength. Among everyone present, only Yun Hao's power could possibly join him in taking down the people from the Upper Realm who were either inviting or intercepting them!
Another reason was that he believed, without any reason, simply as a man's intuition, that Yun Hao was also unwilling to go along with those people.
