I didn't read the chaps in a row so I might be forgetting something, but you gotta think a little in the position of the MC too. You live with a "person" that is supposed to be dead and that can't be removed from the room and she can disappear when others visit. His friend just got killed and you see that person living with you eating innards that may or may not have been taken from your friend.
The beating was a result of not seeing any understanding of the words said before it so I don't think the result was that far fetched. Also being cramped to your apt for a week and not going to school etc can severely impact your sense of judgement. I do hope we get a new revelation soon though, because violence after the first beating is just flavor.