Sorry for my bad memory it might be a little bit inaccurate.
It's a sad story about the main character revisiting his past trauma. When he was younger, a kid had tried countless times to befriend him since he got bullied often. The kid dies around graduation day. After his death, it had traumatized him and the city folk for a long period, causing this town to diminish in value. The main character revisits his hometown after a couple years to settle into a house with his father. He discovers a hidden room with a mysterious telephone that allows him to contact the kid who died from the past. The Main Character tries to uncover more information about the kid in order to save his life before graduation day.

It's a BL manhwa about a chubby-kid in school who confesses to another kid because he was nice to him. After he confessed the guy backed off and started to avoid him/bully him? Eventually, he loses weight and I think he joins the archery club. I think that's where he finds his love interest.
Sometimes this specific manhwa pops up in lezhin advertisements.
Out of control maybe?
I think it is the side story in "never understand"
Yeah that is http://www.mangago.me/read-manga/never_understand/?av=2 the official manhwa title is Out of Control. It's the 3rd couple
ff
Ah, thank you, everybody! ;u; I forgot it was in that manhwa!