https://www.mangago.me/read-manga/cosmic_boy/
i can only think of this^
Suicide boy
No home
Rental onii chan
Shuumatsu no laughter
Reimei no arcana
Suijin no hanayome
Sea foam
https://www.mangago.me/read-manga/the_paper_plane_which_is_under_the_rainbow/
https://www.mangago.me/read-manga/lonely_to_organdy/
And I recommend avogado6 for sad and usually dark suicidal painfully realistic one shots with simple art. Those stories just wreck you
Anything thats sad asf pls i need to cry