Why does Winston so excited by his conversation with O’Brien? Should he trust him?

Winston has dreamed of meeting O'Brien. Winston is speechless when O'Brien stops him in the open to speak with him. Winston fantasizes that O'Brien, an inner party member, thinks like he does. I think there are two sides to Winston here. His rational side knows that any thoughts of rebellion or "the brotherhood" are pure "folly". His emotional side wants to trust O'Brien and rebellion.

Winston is so excited about the conversation with Obrien because it was getting Winston one step closer to rebelling against the party. Which throughout the entire story is what eh strives to do. He is also so excited because of the dream he had 7 years prior. In the dreams he heard O'Brien talk to him and that gave him all the hope he had at the beginning. Also trustung Obrien can be seen as a good idea and a bad one. He pretty much has to trust OBrien because that's all he really has at the beginning. Until he meets Julia all he has is to go off of is a Dream about OBrien that he had seven years ago and when Obrien looked at him during the two minutes of hate video. He eventually does end up trusting Obrien and it does come back and retaliated on him but in the end it was what Winston wanted all along. He wanted to be cured all along. Which is what Obrien helped him achieve. So yes, OBrien does help Winston get better and stop wanting to rebel, but he is also the one who tortures Winston and turns him in.