I want to watch the responses to this too because I've been trying to find it. It may be one that's disappeared from this site :( Good luck to us both on finding it :)
Was it a oneshot from the Joshi bl anthology?
I think so too
http://www.mangago.zone/read-manga/joshi_bl/mf/c007/
Yep! No wonder I couldn't find it. Thank you!
Woah! Thank you so much. That's the title!
Wait -- Found another one -- I liked this one, too: http://www.mangago.zone/read-manga/natura_turaly/
Oops -- no I mean I liked the REST of them.
I don't remember whether it was shounen ai or yaoi but here's the story.
It was about twins that were the opposite gender. (A for the guy and B for the girl)
Then, this guy falls for A and B gets really jealous because everybody always pays attention to A.
Please help me find it! (๑•ㅂ•)و✧