Kimi to Boku no Platonic

Suenaga, a university student, has lost confidence in dealing with people because of past trauma. Encouraged by the words of Koba, a senior he meets at a theater club performance, Suenaga decides to join the club. Unlike Suenaga, who hides his true self and goes along with those around him, he finds himself drawn to Koba who's quiet, sincere, and kind. One night, when the two go out drinking together, a slightly tipsy Koba makes a startling confession...

(Source: Kaiohsha, translated)

Note: Includes one extra chapter.