Koi no Kotoba - Vol. 1 Ch. 7 - A story of yearning.

[MangaDex]

 

[glintel]

people are insanely weird. isolating and bullying people for things that are none of their business...

 

[Fenex2402]

Oooooo
Kids are terrible people

 

[Kaitensatsuma]

Ah, the twittering call of the Japanese Chirping Bitch
So Majestic

 

[HoangDinh]

people are insanely weird. isolating and bullying people for things that are none of their business...

Not really, if Nanakida's successful hook up with Komiya then she wouldn't have snitched. But since it didn't go as planned, she plays victim and blame it all on Yuuri.
She's already in Nanakida's sights (being her crush's crush) + Nanakida's just so happen to have the perfect ammunition - Yuuri's secret adult boyfriend.

And now since the girls know about Yuuri's affair, it is their business, whether it because they just wanna pick on her or it genuinely irks them. You may feel it's none of their concern, but they don't.

If we all followed the same logic, aren't we just fleshy robots?