Maybe greed and lust took over his senses.
from what i remember reading the novel it was because he wasn't satisfied with zhishu sexually cuz he liked it rough but zhishu didn't so he went to get ass elsewhere
Money n power changes people
I could understand the cheating at some point (i mean... its pretty nasty but whatever) BUT the thing is, he never tried to spend time with Zishu. He spent all his time at work and playing around, and spent very little time with Zishu. At this point, i dont understand how that can be love. Obviously, he didnt cherish spending time together.
I wonder if its too late to ask but why did Jiang Wenxu start cheating on He Zhishu? Like since 3 years? JW loves him yet cheats on him?