I need a bl where it starts out of humor or some goofy reson they start fucking but slowly...

https://www.mangago.zone/read-manga/all_about_lust/

Quite literally described this masterpiece. You might have already read it though

https://www.mangago.zone/read-manga/perfect_buddy/

I would say these two fit the criteria (I am also camping here for future responses)

https://www.mangago.zone/read-manga/fujimi_no_meinichi/

https://www.mangago.zone/read-manga/setouchi_kun_ha_hitoriyogari/

https://www.mangago.zone/read-manga/sign_language/

UR DESCRIBING THIS TO A TEE
https://www.mangago.zone/read-manga/you_and_i_can_t_do_this/