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BIFF: There’ll be no pity for you, you hear it? No pity!
WILLY [To Linda]: You hear the spite!
BIFF: No, you’re going to hear the truth—what you are and what I am!
LINDA: Stop it!
WILLY: Spite! (Act 2)
Willy's accusation that Biff is spiting him stems from his knowledge that his son felt betrayed by his affair.