"That's Why I Sigh" is a romantic comedy one-shot by famous shoujo mangaka Ichijou Yukari. It was published in 1993, long after Ichijou's more well-known yuri story from 1972, Maya's Funeral Procession.
At 17 years old, Iketani Kyou is sick of women. They always want to get into his pants, but it's never anything more than shallow (and occasionally creepy) infatuation on their part, so he's pretty dubious about the idea of falling in love and having a real relationship. At one point he thinks, "Ah, God, is it my life's calling to work in a host club?" His plain-featured best friend Hide is the polar opposite. Women never pay any attention to him, bypassing him for Kyou, so Kyou's complaints just annoy him.
Hide gets a crush on an "angel" he's seen (but never spoken to) who attends a nearby girls' school. The girl, a feminine, petite blonde named Rena, is always with her tall, androgynous best friend Mako. After Kyou and Hide have a misunderstanding with Rena and Mako on the train, Kyou discovers that Mako is a bartender at the bar where her father works as a drag queen. Mako likes women (and she's in love with Rena)...but she also hates guys. Kyou asks Mako to help him set up a date between Rena and Hide. ("Don't worry, he wouldn't even have the guts to hold hands with her.") To keep Kyou from telling her school about her part-time job, Mako agrees and she and Kyou go on a double date with Rena and Hide.
Nothing happens between Rena and Hide, but Rena is definitely straight and it turns out that she dances at a ballet company. Each dancer has to sell a certain number of tickets per show, and Mako uses the money from her part-time job to buy out Rena's tickets for her "friends." Kyou sees right through it and when they're alone he tells her that it's wonderful that she's able to fall in love, regardless of whether it's with a girl or not, which makes her start crying from relief.
Kyou can't get Mako out of his head after the date and realizes that he's in love with her. Bottom line: Rena tries to seduce Kyou, Kyou winds up taking her to the hospital instead, some crazy stuff comes to light (with a resolution as unlikely as pigs flying over the frozen fields of hell, but that's manga for you), and Mako gets over Rena and her fear of men. She and Kyou remain good friends and she's still gay. Lalala.
"That's Why I Sigh" is very typical and atypical at the same time. Kyou, Mako, and Rena seem like archetypes in the beginning (cynical playboy; man-hating lesbian; pure, delicate flower) and end as surprisingly complex characters. (And empathetic, in Kyou and Mako's case.) There's a nice balance of humor (mostly of the ironic, observational variety) and realistic drama, mostly involving Kyou falling in love for the first time (and refreshingly, making his feelings clear without pushing them on Mako) and Mako becoming more comfortable in her own skin.
The scene in which Kyou supports Mako's feelings is a real gem and the ending nicely subverts the "gay because she hates men" trope. Rena's soap opera-like subplot is the weakest bit, but the story doesn't dwell on it too much. It's a sweet story, and definitely worth checking out.
Update: Re-posted on scans_daily.