Are you alright with manga? These one fit your description:
https://www.mangago.zone/read-manga/sabita_yoru_demo_koi_wa_sasayaku/
https://www.mangago.zone/read-manga/friend_line/
https://www.mangago.zone/read-manga/no_color_baby/
https://www.mangago.zone/read-manga/ore_no_oniku_chan/
- https://www.mangago.zone/read-manga/voice_of_love/?xIYT
- https://www.mangago.zone/read-manga/my_darling_signed_in/?av=2
(it is not exactly an ex-boyfriend, but like the guy ruined the Mc's life and manipulated and isolated him from the others because he liked him. He comes back when the Mc is happy with his boyfriend, and ofc fails to seperate them)
- https://www.mangago.zone/read-manga/10_years_where_i_loved_you_the_most/
Any bl manhwa where the uke has a trash ex boyfriend then met a kind hearted/treats him well suitor or boyfriend?? I needddd it(╯°Д °)╯╧╧
+ points if the ex boyfriend tries to ruin their relationship but he can't lol. I wanna see trash ex boyfriends struggleeee