Something sad or horror that doesn’t involve romance?
https://www.mangago.zone/read-manga/watashitachi_no_shiawase_na_jikan/
It's a sad manga.
There's mild romance but you can't describe this manga as romantic.
Some people are saying that the author put no effort into the end, but I would say only the last chapter was off. Overall the story was good, not better than the first one, but was still good.