After the apocalypse, Wu Chengyue raised Ling Ling in the drastically changed world. Some people followed him, and they build a base together. Only after that did they finally have a home.
After becoming Ling Ling's daddy, he devoted his off-work time to try and be a good father. At work, he was all about how to be a good leader and how to run the base, providing a safe and comfortable place to live for all the survivors.
In the zombie-free base, people had food, clean water, and places to live. All these needed him and the other two leaders to spend efforts on.
As more and more people joined his base, more problems occurred, and he became busier and busier. So, he had no spare time and energy to think about starting a relationship.