I HATE the author's decision here. Just make the classmate a judgmental jerk. He could've just been an okay person. He could've been hurt that Eiji hid something from him when he thought they were friends. Instead, the author chose to make him a jerk because it's easier to write an external negative force to push Eiji ahead instead of actually having Eiji realize anything on his own without Aoi coming in to say the same damn thing she has been saying since the beginning.
It is cheap. It makes it look like crap.