Responses
Dust diamond -> a manhwa
Our happy ours -> manga but short dw
Siren's lament (on webtoon its a masterpiece but more dramatic than sad)
https://www.mangago.zone/read-manga/nemurihime_yume_miru_you_ni_koi_shiteru/
Not a list, but I highly recommend it (⌒▽⌒)
sad romance list please. preferably straight, although any is fine :)