I need one of those bl mangas that start out when they're kids and is a genuine slow burn ...

Park Hanhoo's Manager
https://www.mangago.zone/read-manga/park_hanhoo_s_manager/

https://www.mangago.zone/read-manga/kimi_ni_wa_todokanai/
https://www.mangago.zone/read-manga/omega_complex_1/
https://www.mangago.zone/read-manga/hikaru_ga_shinda_natsu/
https://www.mangago.zone/read-manga/salad_days_tang_liuzang/


ik that you said you only wanted bl mangas but I genuinely think these are some of the best childhood friends to lovers series ever written, and I do rlly think you'll love them:
https://www.mangago.zone/read-manga/kodomo_no_omocha/
https://www.mangago.zone/read-manga/last_game/
https://www.mangago.zone/read-manga/i_love_you_baby/
https://www.mangago.zone/read-manga/nekota_no_koto_ga_ki_ni_natte_shikatanai/

THANK U SO MUCH BOTH YALL ILY ε=ε=(ノ≧∇≦)ノ