I think it was Shoujo with a girl (A) and the male lead (B), but then his brother's girlfriend/fiancee/wife(C) suddenly appears and B is still in love with C while the C only love B's brother. Later C returns to B's brother and you see C run towards B's brother who's standing on a staircase. (〜 ̄△ ̄)〜
it's a shounenai but.... this has the scene you described http://www.mangago.zone/read-manga/seven_days/
I only remember one thing. There's a girl who likes a guy, but the guy is smitten or tied to his brother's wife/girlfriend. In the end the wife returns to her husband and she is seen running towards her husband who is standing on a staircase. He holds out his hand and she places her cheek in it.
Well, there's a scene identical to the one you describe in a shounen ai!
The manga is: http://www.mangago.zone/read-manga/seven_days/
And the scene you described: http://www.mangago.zone/read-manga/seven_days/an/seven-days-chapter-9.html/16/
The author of the manga has similar artstyle as another author (I think they're siblings? The manga is about a painter and a girl who ends up modelling for him? In one of the scenes she is sitting on the bed (in a fetal position) and sleeping. ( ̄∇ ̄")
totally guessing here but - http://www.mangago.zone/read-manga/hakuji/