Responses
I remember these:
Chap 1 and 6 of: http://www.mangago.zone/read-manga/suki_ni_naccha_ikenai_hito/
And the whole manga:
http://www.mangago.zone/read-manga/i_want_to_become_your_bird/
First story of this is about this guy in love with his sister's fiancé:
http://www.mangago.zone/read-manga/last_portrait/
And in Chap 5, the main character is in love with his bro's boyfriend!!
http://www.mangago.zone/read-manga/mata_kite_shikaku/
Any yaoi with
Uke or Seme falling in love with his sisters boyfriend? ^^