What really hit me here was how Watari realized that he wad becoming a better person... all for the sake of the girlfriend that he loved, so when he lost the girlfriend that was the root of his motivation, he didn't have the enough self-confidence nor the friends to help him appreciate all the effort, goals and progress that he had achieved so far, making him feel lost in what he was and what he could do.
You guys may not notice, but when you're going through a rough psychological patch and undergoing a long-term quest for self-improvement, losing your main motivation and not having anybody to fall back into can be deadly for your progress, not to mention your very own psyche.