It wasn't the apocalypse that broke him. He was strong enough to survive that. But when his childhood friend died for him, that was when Lu Hao realized he had made a mistake. Now he had a chance to fix it.
(This is an expansion of the story "At the End of the World", as told by Lu Hao. It is told in three parts: arc 1 involves Lu Hao and Hong Sheng's childhood. Arc 2 delves into the original events of the first timeline, which resulted in Hong Sheng's death. Arc 3 shows how Lu Hao uses his second chance when he wakes up before the apocalypse - before Hong Sheng dies.)