Why did Rodwill commit suicide?

In Part Three, we learn that Rodwill was transferred to the front. When he gets there, he finds the men in the trenches have gone mad..... they were methodically killing rats, cats, and whatever else they could find. Rodwill tried to stop the men, something which provoked his fellow soldiers to force him to watch them kill a cat. Within a half hour, Rodwill shot himself.