Responses
Maybe this one? It sounds similar but the only difference is that the main characters was never together, but only had a one night stand
http://www.mangago.me/read-manga/i_fell_in_love_with_my_girlfriends_brother/
i am looking this type of manhwa where the mc uke broke up with his bf. but years or months(?) later.... The ex-bf comes back but in a relationship with the mc's sister. but after meeting again it seems the ex-bf still in love with the mc uke, and yet the sister seems kinda sus.
its a colored manhwa. chinese manga i guess?
Thanks if you link it here