Tsugou no Ii Onna

Fuji, who's gay, does his best so that one day he can make love to a girl. But, he's unable to do it and his girlfriend dumps him. The next day, he goes to his school club reunion, where he's reunited with his first love and first boyfriend, Kana... Come morning, he wakes up to find Kana sleeping next to him in his ex-girlfriend's lingerie!

(Source: Renta!)