First, Xiao Hai had a mutual affectionate partner, and they had reached the age to talk about marriage. No matter what, sleeping with another woman by accident—the fault lies with him.
Xiao Zimo is a man, and he understands that no matter the situation, as long as one is determined and has a woman in their heart, they wouldn't touch other women. When he still touched Su Lin while having a partner, it means he was tempted—there's no doubt about it.
Secondly, he couldn't treat the two children equally. He shouldn't have said that he wanted to bring Xiao Zimo back to the Xiao Family and raise him.
The result was that no one was happy.
Thirdly, as the high-ranking commander of the military district, he casually believed in rumors and didn't seek out the truth. He didn't even discover the affair between Xiao Qing and Shen Yuexin under his own nose.
He had long been blinded.
A larger part was due to believing the gossip around him.