19 days and cherry blossom i can recall off the top of my head but you've probably already read them. There's "nan hao and shang feng" but it's not BL although there's potential for shipping them
Then there's sasaki to miyano and doukyussei as well. There's another one with a weird teacher student couple but I forgot it's name. "green apple" too but it doesn't have many volumes
I think it was something my hero, I don't remember clearly
I remember now. It was hitorijime my hero
https://www.mangago.zone/tag/long+story/
I'm sure not all these are BL but there's some great reads along the way.
Any good slice of life bls manhwas that are long and have lots of volumes? Especially the ones when it's starts from their highschool life to their adulthood xxd