There's a little bit about bullying in this one. It's mostly about grief and learning how to live with it. It's really good though. Highly recommend.
https://www.mangago.zone/read-manga/happy_birthday_1/
Bullying but the mother of the child is taking revenge. https://www.mangago.zone/read-manga/maria_no_danzai/
This one is good but I dropped it around the 100th chapter because I thought it was getting dragged on but it might be your thing.
https://www.mangago.zone/read-manga/juujika_no_rokunin/
I loved this one.
https://www.mangago.zone/read-manga/ijimeru_aitsu_ga_waruinoka_ijimerareta_boku_ga_waruinoka/
can anyone give manwha recos similar to Save Me? like about bullying and sad stuff