I would highly recommend you, trying "Crush on You" by Lee Kyung Ha. Seems to fit several of your criterias.
http://www.mangago.me/read-manga/crush_on_you/
that's a very specific storyline, lol however do look around my bi list, i keep similar stories for personal interest http://www.mangago.me/home/mangalist/68052/
I've read this manga http://www.mangago.me/read-manga/illumination/an/illumination-chapter-5.html/2/ where a girl and her male classmate are interested in the same guy, and it got me thinking... Are there any other mangas like that? Not Koi to Uso, cos I heard there was something like that which was downright heartbreaking. Something like this one, where a girl likes a guy and she finds out his male bestie is also into that same guy: http://www.mangago.me/read-manga/atashi_wa_bambi
I'd wanna see a yaoi setting like this: guy A likes guy B, and another girl likes guy B as well. And if guy B swings both ways, there's a chance he'd go for either guy A or the girl. (Maybe like 7Days, where the seme was still hung over some chick)
I'm curious if there's something like that where the rivals get a FAIR shot at the person they like, making it hella exciting to root for the side we want to win... not something where the girl will get the guy cos her male rival is a comic relief gay character, or if a girl gets a girl she likes cos the male rival is a chauvinistic jerk, or if a guy gets the guy because it's yaoi and the girl will be some horribly written shrew of a woman. Though to be fair, the guy will have to win the guy if it's yaoi, girl wins the girl if it's yuri and girl(or guy) wins the guy(girl) if it's shoujo.
I just want a bit of a rush when i read it i guess ╮( ̄▽ ̄)╭