I would describe Winston's attitude toward O'Brien in this chapter as a mixture of both fear and admiration. Orwell uses specific verbs and adjectives here to paint O'Brien with a specific air of confidence, while Winston is portrayed as jittery and eager. This is especially clear in the middle of this chapter, when O'Brien asks Winston a series of questions to test his allegience to the Brotherhood: "...You are prepared to commit murder," to which Winston answers, "Yes."
Winston admires O'Brien for being a part of the "Brotherhood" and is willing to do almost anything to join or serve him for this important cause. O'Brien shmoozes Winston and Julia by serving them wine and then fascinates Winston when he is able to complete the stanza that Winston often repeats.
Overall, I would say that O'Brien is both a symbol of hope and fear in Chapter 8. He represents the idea of a future when they can finally be free from the telescreen and the other confines they currently know, yet he also represents risk. Opening up to O'Brien is the most drastic measure Winston has taken so far against the Party, and he knows this, yet he chooses to proceed.