I guess he's ignoring that other dude's advice to him about not opening old wounds. He's definitely going a bit nuts here though, this isn't a conversation to have while agitated and emotional. Maybe it's not even a conversation to have at all. That would be crazy though, if the uncle really does like and is attracted to Hotaruko, the child of the person he had an affair with and obviously was intimately involved with her sometime in the past when she was what, in middle school or even earlier? Phew, even for manga that's pushing it.