I think it was the "just... neighbor" part that got him. "Friend" could get upgraded by adding "boy," and "relative" after they get married. But, Matsuo saying Yukki's "just so and so neighbor" is kinda
Yes. Yes, I do comment in paragraphs. 
Dads, uncles, brothers, oh my! Check out list of (mostly) BL with kids: https://mangabuddy.com/manga-list/46295
Dads, uncles, brothers, oh my! Check out list of (mostly) BL with kids: https://mangabuddy.com/manga-list/46295