DISCLAIMER: I think this is yuri but there's no guarantee, it could be a het I misremembered as yuri
I think it was angst, or at least drama. Story consists of MC, GirlA, and Senpai. MC and GirlA I believe are good friends. Anyways MC is in love with Senpai and MC was open about it to GirlA. MC noticed that GirlA was in love with MC but tries to convince herself that Senpai was her love and try to ignore GirlA's feelings. Eventually MC decides to confess to Senpai and told this to GirlA where she saw GirlA obviously disturbed by this but tries to hide it (albeit poorly). Something happened with Senpai and then MC realizes that GirlA was the one for her or something. I forgot the ending, whether it was a good ending where MC and GirlA got together or whether it was a sad regret ending where it was too late and GirlA ended up hooking up with someone else.
It was a oneshot but I forgot if it was a Original oneshot or a Doujin of some Manga/Anime. And as I said I'm pretty sure it's yuri but there's no guarantee since I don't remember too well. GirlA could've been BoyA for all I know about (I'm confident that the MC is girl atleast tho). Dunno if this will help but IIRC MC is an outgoing girl, GirlA is a not too confident in herself (though not sure if you'd describe her as shy), while Senpai was the typical nice/kind hearted girl.