In school, all the relationships Harry sees are teenage ones, and the only healthy adult relationship he has seen is the Weasleys (very parental). Seeing a healthy adult relationship in someone he considers a friend (Nathaniel... did I really just call Anita and Nate's relationship healthy? Break out the ice skates) is a real eye opener for Harry. In this setting, he's the youngest of the bunch, and that's a very different sitution from Hogwarts. It's good for him.