Was the person hanging out with Eita at college, Nakajima?
In the credits of episode 12, TAKANASHI Kengo is credited as voicing Nakajima. The character who speaks to Eita at the end of the episode could not be any of the other credited characters (the only unnamed ones are "wind band junior A", "wind band junior B", and "track-and-field junior", clearly none of whom are this character), so unless this character's voice actor went uncredited, he's Nakajima.