What convinces Winston that O'Brien shares his feelings against the party?
Winston's first indication that O'Brien is on his side is in the first chapter, at the end of a 2-Minutes Hate, when his and O'Brien's eyes meet briefly. Winston feels that the quick meeting of their eyes was confirmation that O'Brien felt the same way he did. O'Brien purposely leads Winston to believe then that he is on Winston's side against the Party. In Part 2, ch. 6, O'Brien has a conversation with Winston and uses the excuse that he has an advance copy of the new Newspeak dictionary and asks Winston if he'd like to see it. He gives Winston his address so Winston can stop by O'Brien's house to see the book. Winston realizes this is only a ruse so that O'Brien can give Winston his address. Two chapters later, Winston and Julia both go to O'Brien and tell him they believe he is part of the revolt movement and they want to be a part of it, too. O'Brien asks them several questions to test their commitment and gives them a copy of Emmanuel Goldstein's manifesto against the Party. They are completely convinced they have an ally in O'Brien. They don't realize the book is something written by the Party just like Emmanuel Goldstein is a fictional character created by the Party to ferret out those who are against the Party.