This one definitely
https://www.mangago.me/read-manga/stardust_family_official/
And I read this years ago but the ending still gets to me:
https://www.mangago.me/read-manga/hana_haru_seok_woo/
https://www.mangago.me/read-manga/itou_san_kuraka_sui/
I almost didn't recover. It's truly disturbing but a damn great read.

Guys what's a manga/manwha you read that destroyed you? Idk im js craving some post read clarity- like u finish a story and ponder ur life decisions.
Some of the ones i liked were This Witch of Mine and June Peach!