Here's a page from the original story showing Tsuyuhiko smiling on the right while Natsurou's ex and his bf at the time are kissing http://www.mangago.zone/read-manga/wonder_border/mrk/mpn_chapter-2329313/pg-18/But hey, that's just a theory
kinda farfetch but okay
Idk he's kinda suspicious
Here's a page from the original story showing Tsuyuhiko smiling on the right while Natsurou's ex and his bf at the time are kissing
http://www.mangago.zone/read-manga/wonder_border/mrk/mpn_chapter-2329313/pg-18/
But hey, that's just a theory