Tom imagines Aunt Polly's reaction if he were dead. What causes these thoughts?

When Aunt Polly returns, she immediately begins to beat Tom. When she learns that it was Sid who was at fault, she doesn't apologize but instead justifies her beating, though inside she longs to say something loving to Tom. Tom, conscious of his Aunts ruefulness yet refusing to acknowledge it, wallows in self-pity. He imagines his own funeral, and begins to cry to himself, reflecting that he leaves the house when his cousin Mary enters the house, unable to withstand any ounce of happiness.