BOYS RUMBLE

For Saijou Misao, a high school teacher in his thirties, love has become such a distant concept for him that even his students make fun of him for it. One night, while drinking alone at a bar, he runs into Takashi Ryouhei, a teaching materials sales rep that he barely knows. However, he's never seen Takashi look like this before...

(Source: Ichijinsha, translated)

Note: Chapter count includes an extra.