I'm trying to remember a Yaoi manga that revolves around a man who replaces their dead brother (could be twin) for healing his late brother's boyfriend, Who I believe he was already in love with. But I believe they fall in the with each other in the end. I barely remember the manga.
Might not be this, good read anyways
http://www.mangago.me/read-manga/nights_before_night/
I hate to say it, but it not the manga I was thinking of. But I have read this one and its a really good manga. But the one I have stuck in my head is more on the substitute side of things. Like I think the twin blames himself for his brother's death, that he forces this relationship upon his late brother's boyfriend. (I believe).
Could it be this one maybe? The dead one was a girl but somehow it fits? http://www.mangago.me/read-manga/kimi_no_naka_ni/
I've posted it before but unfortunately no result in finding the one that has my mind in stitches. Its a yaoi manga, the main Character had twin brother who died. Thee said twin had a male partner. So after the death of the brother, the main Character takes his place and becomes the replacement taking par of the relationship. Because (I believe) he blames himself for his brother's death. And (I think) he already loved his brother's lover to begin with, or started when he became the replacement. Its been killing me trying to figure out which manga this is. I want to say this is a short manga, or from a manga that is piled with oneshots. But then again I could be wrong.
Ive read those and it truly heartbreaking.. sorry i also forgot the title.
is Dakedo, Ashita no Hanashi o Shiyou http://www.mangago.me/read-manga/dakedo_ashita_no_hanashi_o_shiyou/ the story you are looking for?
OMG! YES! I truly believe this is it. Thank you so much, you have no idea!