Do you know any manga where the seme used to sleep around, but after meeting the uke, he became completely devoted to him?
https://www.mangago.me/read-manga/mukoiri_alpha_wa_ai_shiru/
another one is waterside night. didnt finish it bc it was bit too triggering for me but from what ive heard, he became an absolute househusband by the end
Can you recommend any yaoi manga where the main characters are childhood friends, get separated, and fall in love after reuniting?
Surprisingly, there aren't many BLs with that premise (that I know of). This is somewhat similar:
https://www.mangago.me/read-manga/bokura_no_tsuzuki/
Also this if you don't mind manhua:
https://www.mangago.me/read-manga/leo/
But in both stories the protagonists reunite during high school. I wish there was something where they reunite as adults. Maybe someone else knows one.
Do you know of a manga with a neighbour or something who knows the seme as a child and later gets together with him?
Seme also had a crush on the uke as a child, I think. But it wasn't grooming! So the uke just thought Seme was cute as a kid!
This one? https://www.mangago.me/read-manga/home_tsuyuki_yuruko/ (idk, if this is what you are asking for but, I find the age gap huge, but... shakes my head in * this witch of mine * )
Do you know any yaoi or shonen ai fanfic here with Satoru und Suguru? (=・ω・=)
https://www.mangago.me/read-manga/patonaga_zenzen_okinakute_komaru_jujutsu_kaisen_dj/
https://www.mangago.me/read-manga/jujutsu_kaisen_dj_saiai/
https://www.mangago.me/read-manga/jujutsu_kaisen_dj_terminal_lucidity_eng/
https://www.mangago.me/read-manga/let_me_in_jujutsu_kaisen_dj/
https://www.mangago.me/read-manga/kimi_ni_sasagu_jujutsu_kaisen_dj/
https://www.mangago.me/read-manga/jujutsu_kaisen_dj_kura_no_ryuukeichi/
Yes, I know a website for more but I don't know if I can share it or not

Do you know any yaoi manga with an age gap? The age difference can be large, but both characters have to be at least in their 30s, or it feels icky to me.
Sugar daddies are also good!
No kink shaming
“How sweet is a sugar daddy” is a timeless one, i dont remember the ages but they’re both adults
Thanks!