I'm looking for a romance shoujo manga that starts off all sweet and sappy between the girl and boy until one of them dies, the end. I don't want one where the other living person's life is talked about after the death and I also don't want one where they find new loves and get over their previous partner. I want sob-worthy tragic endings. Thank you.

Maybe Bokura no Koi wa Shi ni Itaru Yamai no You de, everything is sad and tragic, even the ending is tragic.

[img]https://i.imgur.com/6MBFpsv.png[/img]
ᵂᵃʳᵘᶦ ᴷᵒᵗᵒ ˢʰᶦᵗᵃᶦ ᴳᵘᶦᵈᵉ | ᴳᵉⁿᵉʳᵃˡ ᶦⁿᶠᵒ | ᵂᵃʳᵘᶦⁿᵉˢˢ

I second Bokura no Koi wa Shi ni Itaru Yamai no You de.
However it is quite dark and twisted so I would like to recommend you something lighter.

Zekkyou Gakkyuu has two particular short stories
that deal with the death of the male/female lead.

• chapter 3.3 "the ocean is calling"
• chapter 34/35 "hell's clock"

Furthermore I strongly recommend Toukyou Lastochika.
A historical manga that 100% fits your description. 🙂

Rec - Kimi ga Naita Hi and maybe 49 (I don't remember if it shows much after he disappears). And seconding Toukyou Lastochika.