https://www.mangago.zone/read-manga/psycho_young_dream/ this one os complicated but to tell you why ials major spoilers. They definitely don't end up together but I don't remember if one of them dies
https://www.mangago.zone/read-manga/kokoro_o_korosu_houhou/ i don't think thwy end up in the end but I'm not sure, anyways this one is reaaaally toxic and abusive
https://www.mangago.zone/read-manga/obey_me/ technically, this counts? I mean they don't end up together and no one dies, but it's like, really shitty. In a fun way
https://www.mangago.zone/read-manga/this_ending/ (not exactly break up but it is uncertain if they will eventually)
https://www.mangago.zone/read-manga/usotsuki_wa_shinshi_no_hajimari/ (manga, uncertain ending(?))
genuine question if there is a bl manhwa out there where the couple doesnt end up together? not bc one of them died but bc they think its better if they werent together kind of story,,if so pls recommend thanms