Responses
Ohh I know a few like this but not this exactly I think.. uh I’ll add them here
https://www.mangago.me/read-manga/their_circumstances_sria/
This one isn’t the story but it’s kinda like that
i'm sorry, but it wasn't any of them, but i don't know if this helps narrow it down, but the sister gave her brother a piece of jewelry that was from the ex and i believe when the ex sees the piece of jewelry he takes it back.
ok, so this might have been the side story, i don't quite remember, but this guy likes his sister's ex, but the ex is still in love with the sister