There is a few manga if you don’t mind!
https://www.mangago.zone/read-manga/the_time_of_the_terminally_ill_extra/
https://www.mangago.zone/read-manga/the_red_sleeve/
https://www.mangago.zone/read-manga/gorae_byul_the_gyeongseong_mermaid/
https://www.mangago.zone/read-manga/this_witch_of_mine/
https://www.mangago.zone/read-manga/the_horizon/
https://www.mangago.zone/read-manga/when_the_flowers_bloom/
https://www.mangago.zone/read-manga/an_uncomfortable_truth/
https://www.mangago.zone/read-manga/timeless_melody/
https://www.mangago.zone/read-manga/10_years_where_i_loved_you_the_most/
https://www.mangago.zone/read-manga/dead_flowers_dami_zetson/
https://www.mangago.zone/read-manga/dancing_with_the_devil/
https://www.mangago.zone/read-manga/momentum_park_ji_yeon/
https://www.mangago.zone/read-manga/perle/
https://www.mangago.zone/read-manga/goodbye_mom/
https://www.mangago.zone/read-manga/what_i_decided_to_die_for/
https://www.mangago.zone/read-manga/teenager_younghwa/
https://www.mangago.zone/read-manga/dark_heaven/
https://www.mangago.zone/read-manga/rental_onii_chan/
https://www.mangago.zone/read-manga/watashitachi_no_shiawase_na_jikan/
https://www.mangago.zone/read-manga/asagao_wa_yoru_kara_saku/
https://www.mangago.zone/read-manga/my_broken_mariko/
https://www.mangago.zone/read-manga/hate_no_kouya_de_vacances_wo/
https://www.mangago.zone/read-manga/paradise_view/
https://www.mangago.zone/read-manga/devil_and_song/
https://www.mangago.zone/read-manga/boku_no_gemini/
https://www.mangago.zone/read-manga/golden_days/
https://www.mangago.zone/read-manga/soloist_of_the_prison/
https://www.mangago.zone/read-manga/kimi_to_tsuzuru_utakata/
https://www.mangago.zone/read-manga/composing_spring_in_this_room_where_cherry_blossoms_bloom/
Can someone recommend a really sad manhwa. Like extremely sad but with a happy ending.