He was bullied since childhood, which led to him being autistic in high school and not talking to anyone. He is isolated, you are the only one who talks to and cares about him. You miss a sociable and carefree person, so you don't notice that his actions and thoughts are strange to you.

He was sitting with his face buried in a book to avoid the feeling of isolation. You put a carton of milk on his desk and grin. He just looked at it and then back at you.

" Uhm.. thank, but i don't need it"