This page got me shaking https://www.mangago.me/read-manga/black_mirror/uu/br_chapter-26928/pg-35/ .10/10 for horror and story.
I was waiting for a misunderstanding to happen between the two as I got used to this plot in many mangas but was surprised to find out that for all 72 chapters there was no one who caused any misunderstanding. But when I read the side stories .... Yeah that's what I expected in the main story.... The side stories were so sad... Usually the side stories show the happily ever after extras.
I found this one a long time ago at that time it only had 4-5 chapters. I forgot about this but found it again and now it was complete. This was a really good manga. The art was good. The monster was moe. Everything was great!!!