Freefall Romance (2004)

Blurb:
Youichi Nanase has a huge problem. His adorable little brother attends an all boys’ school—one that is rumored to have a 90% gay student population! Fearful for his brother’s “safety,” Youichi spends his nights drinking his woes away with his coworker, Renji Tsutsumi. But Youichi’s brother isn’t being pursued by his classmates; he’s the one doing the chasing and he’s finally captured the heart of his volleyball teammate. To make matters worse, Renji himself has fallen deeply for Youichi! Will Youichi finally be able to accept his brother’s relationships with men and find a love of his own in the process?

Source: www.anisearch.com/manga/3902