Raising Beta is the only manhwa I can remember that had this trope. It's revealed near the end.
https://www.mangago.me/read-manga/raising_beta_winnow/
You might have seen popular ones I will give an old yaoi manga reason it's 2nd story which will come after 1st story end in this one seme hired one guy who bullied uke in school and stole uke's fiance so he could come back to him here-
https://www.mangago.me/read-manga/mezame_no_mori/
Pretty wholesome at first!
https://www.mangago.me/read-manga/ore_no_aoharu_wa_watasanai/
Not wholesome at all! Actually kinda dark!
https://www.mangago.me/read-manga/lima_syndrome/
Also, it doesn't completely match your description, since it isn't the seme doing it, but My Darling Signed In does have a plot thread of being bullied in school at someone's request!
https://www.mangago.me/read-manga/my_darling_signed_in/
Not exactly bully but the seme did something so uke will be dependent on him. It's called orchestrated dependency or mind breaker
- http://www.mangago.me/read-manga/imitation_mate/
- http://www.mangago.me/read-manga/gintama_dj_mienai_kusari/
- http://www.mangago.me/read-manga/hikizuru_oto/
- http://www.mangago.me/read-manga/akuma_chan_wa_momoiro/
- http://www.mangago.me/read-manga/seishun_kinema/
- http://www.mangago.me/read-manga/lovely_play/
- http://www.mangago.me/read-manga/miteranneeyo/
- http://www.mangago.me/read-manga/seito_no_shuchou_kyoushi_no_honbun/
- http://www.mangago.me/read-manga/10/
Looking for some BL where seme hired/asked some people to bully uke? The reason being so uke would only have seme to lean and rely on