I think he likes him so much because the comment at one point in the beginning where he says that despite the turmoil he feels he still has a pure heart. In general Demons, no matter the story it seems lol, at least one of them has a thing for a pure hearted person.
The thing with his family was a little abrupt I admit, but they did kinda set it up showing how he came home with his own food, showing no one cooked for him, and when he greeted the house no one noticed. Basically it seemed he was a child from an old marriage (guessing that since the uke says he doesnt want that woman in his house.) and to his family he was in the way of the old one. His family sucks basically.
Anyway, hope I helped :D
I feel like I missed something at the begining...why does sensei love him so much.and that whole thing with the uke's family is kind of abrupt.Am I the only one?