There's so many but they're so toxic, do you still wanna read them?
The toxic part is that usually the seme in them are either little children while uke being like really old [obviously nothing happens between them before time skip] and sometimes even inc*st, I'll drop them if you're fine with reading that kind of stuff (⌒▽⌒)
December (i’m sure this is the exact story you’re describing though) ╮(￣▽￣)╭
feel free to drop themmm ive been searching for more tropes like these
Ok! Here ヾ(❀╹◡╹)ﾉ~
Placebo (yaoi)
Sankaku Opera
Toshi no Sa x Omegaverse BL
Hunting Game
Miscreants And Mayhem
Sayonara Alpha
Dear teddy bear
The Tiger Who Swallowed The Moon
ENNEAD
Iki o Hisomete, Koi o
Color Recipe
Fuson na Hana o Aisureba (seme and uke are same age I think but this story is really creepy for a lot of reasons)
Haven
EGOISM
Onii-chan Datte Amaetai Wake de
Not equal
Mayonaka no Oyatsu (Yaoi)
Ibitsu no Kakera
Ienai Itami o Daite Iru
An Uncomfortable Truth {not bl but kinda shounen ai but it's so fcked}
Save me (no romance but so much obsession between brothers)
Dispar {discontinued by author}
The Inheritance of Aroma (I bet you'll need a jumbo pack of tissues for this one)
Enjoy (≧∀≦)
Tell me if you need more
grumpy x sunshine bl story ???
recs bl with mc meets ml when they were young, but mc is slightly older and they have a reencounter in the future where ml is obsessed with mc