Uchi No Wanko Chōkyō Sakusen summary:

Yuki is a salaryman who loves men to his core, and Shibasaki is his junior who adores his master like Hachiko. The two, having just started dating, tried to have s**, but it ended in failure.... The reason: Shibasaki's lower half wouldn't get hard. "You're the one who confessed to me, aren't you? If you like me, why can't you get an erection!?" Shibasaki tries every trick in the book to get an erection, but....+