Actually, Bai Zemin did not really leave but played a little trick to deceive the three girls.
Given the difference in power between the two sides, deceiving Cai Jingyi and Nangong Lingxin was something Bai Zemin could do without much difficulty. However, deceiving Kali was a completely different matter.
Unlike 99.99% of soul evolvers, Kali did not use her eyes as her main sense to perceive her surroundings. Furthermore, she was the only existence within Bai Zemin's knowledge with the ability to see the souls of other living beings.
Putting aside the fact that Bai Zemin's Invisibility skill was unavailable as were most of his active skills, even if he could use this skill it would be of no use against someone who did not rely on the five general senses unless, maybe, the skill were upgraded to its highest level.
Bai Zemin squatted down and touched the drops of red blood with his hand.