I have only seen the anime versions of these manga but the saddest I’ve seen would be Anohana and Your Lie in April
https://www.mangago.me/read-manga/hoshi_mamoru_inu/
https://www.mangago.me/read-manga/phony_world/
https://www.mangago.me/read-manga/mouth_to_mouse/
https://www.mangago.me/read-manga/boku_no_gemini/
https://www.mangago.me/read-manga/last_day_1/
https://www.mangago.me/read-manga/my_broken_mariko/
https://www.mangago.me/read-manga/maria_kero/
https://www.mangago.me/read-manga/when_you_grow_up/
https://www.mangago.me/read-manga/teenager_younghwa/
home far away
into the rose garden
https://www.mangago.me/read-manga/timeless_melody/
This is basically the notebook but gay
I need a good cry, please recommend the most heart wrenching, gut wrenching mangas that will absolutely make someone cry buckets