if my memory is correct then try out https://www.mangago.me/read-manga/december_rain/, if you want heavy angst you should also check out Erha and Yuwu, they're novels though
https://www.mangago.me/read-manga/haru_wo_daite_ita/an/haru-wo-daite-ita-chapter-24.html (not the main story, only Winter circada ch.24+25)
I need a recommendation of two lovers or mcs (doesn't have to be romance) that died at the end of the story. No happy ending, because everyone dies, don't recommend me aot pls, I already read it and love it.