Futari no Himitsu (TAKARAI Saki)

From Shinmakoku Scanlations :

The visually handsome guy, Ayumu. His anguish is only one, his "thing" is phimosis. He doesn't like a certain classmate who's even more popular than him, Oosawa. For no reason, Ayumu believes that Oosawa might be a "fellow" patient, and he desperately stalks him to proof it. Ayumu's desire to see Oosawa's crotch is becoming unstoppable.

And the "Too Early for Children" series...
The love story of 4 couples, taking a stage in the bar is also included.