Sono Hada no Atsusa wo Oboeteru

Hairdresser Gen has feelings for his older childhood friend Kotaro, who is in love with his older brother Kanade.
One night, after hearing that his brother might get divorced, Gen spends the night with an overly drunk Kotaro in a hotel, and becomes excited, thinking that there might be a chance for him.

However, Kotaro mistakenly thought that he had slept with the brother Kanade, not Gen. Gen is used to being mistaken for his brother Kanade, but when he finds out that Kotaro had mistaken him for his brother Kanade even during the night they shared, his heart swells with discontent... A bitter, one-sided love story between childhood friends, a young, handsome, but troubled hairdresser, and an older, naturally charming, but plain-looking boy.

(Source: Hakusensha, translated)

Note: Includes 2 extra chapters.