Look at Me.

"Sorry I'm not a girl." Turns out, I knew nothing about Saku. Kyosuke had always thought that his childhood friend was a girl. And he was likely already in love by the time he realized that Saku was a guy. Thinking that this kind of attention from another guy would only annoy him, Kyosuke decided not to pursue Saku. But one day, he noticed hickeys on Saku's back... Thus began a tale of earnest love that would take a turn for the worse.

(Source: Renta!)