oh you got the wrong name AHAHHA it's "nan hao and shang feng"
This one is not BL but the art style is quite similar and there is a girl in it who ships the 2 main characters, the title is also similar to the one you said http://www.mangago.zone/read-manga/nan_hao_shang_feng/
tell me why I was looking for that too and i was gonna throw my computer cause I couldn't find it or the damn tiktok again so I just searched it up and turns out one of the letters was wrong, anyways who knew the book was actually great I saw it so many times but I thought it was boring
i saw a bl manga on tiktok and someone said the name of it was "nan gao shan feng" but i didnt find it but it had the same art style as 19 days maybe even the same author so if anyones knows what im talking ab pls lmk:)