have u tried: 10 years where I loved you the most?
Black lotus
they also said that this is sad.
http://www.mangago.zone/read-manga/my_fiance_is_in_love_with_my_little_sister/
Im sorry in to lazy to provide link , just search their names
I highly recommend Tamayura (manga) and December Rain (manhwa).
Happy crying!
need some sad bl that will make me cry :)