http://www.mangago.zone/read-manga/almond_o_nanatsubu/
http://www.mangago.zone/read-manga/tied_up_in_twins/?av=2
i can't find that one story about the dead twin and the coping between the boyfriend and the brother but it definitely left a bitter taste in my mouth lol
special mentions, close to what you're hoping for but sorta different
http://www.mangago.zone/read-manga/koinegau_horizonte/
http://www.mangago.zone/read-manga/soine_lovers/uu/tr_chapter-5/pg-1/
http://www.mangago.zone/read-manga/sora_o_daite_oyasumi/
Do u mean this?
No, it was a story about the surviving twin pretending to be the dead twin despite the reluctance of the boyfriend. When they have sex, the boyfriend calls out the name of the dead twin. Anyway, it was an unhealthy way of coping for the two. The surviving twin had survivor's guilt so he was sorta punishing himself. It ended pretty half-assed where the surviving twin and the bf got together for real.
Did you ever find it the story you were looking for? I've been trying so.hard to find it too.
If you mean the one I was talking about, I think it’s this:
http://www.mangago.zone/read-manga/dakedo_ashita_no_hanashi_o_shiyou/
Omg YES
Any yaoi manga where seme actually loves someone else but uses or stays with uke instead? Anything is fine, as long as it has something similar to it.