Kitto Kiss o Suru Toki by KANDA Neko [Eng]

Plot:
Shin has always cherished his little brother, Satoru, and his childhood friend, Mitsuya. But when he overhears a group of fujoshi fantasizing about the two kissing, he starts feeling strangely conflicted. Convinced he’d be fine if they were together, he brushes it off—until he actually catches them in the act. To his surprise, instead of feeling happy for them, tears start to fall… Why is his heart aching so much?