Delinquent Daddy and Tender Teacher

This is a sweet story, but why is their bond rekindling so fast? They haven't met each other since high school, when Hitsuji used to have a crush on Hatoyama. But they somehow met again and tried to befriend each other, and Hitsuji tried to help with Hatoyama's life and stuff like that. Why would he help his old crush like that? And why would the delinquent guy have a kid with him when he's incompetent? If a parent is that incompetent while being the kid's only parent, the child protective services would already have intervened. And I think they probably would date and forma family together, but why? If Hatoyama didn't like Hitsuji in the past, why would he like that guy now? And why would Hitsuji have the chance of liking Hatoyama again when crushes only happen once per person to anyone someone meets in life? I don't really see much personality or traits of any of the characters. But still, it's a sweet story.