For what reason does Winston believe that O'Brien has talked with him? What are his feelings about this as the chapter ends?

In Part Two, Chapter Six, O'Brien approaches Winston and
strikes up a conversation. For Winston, this moment is a significant one. Not only does
Winston sense that O'Brien's "political orthodoxy was not perfect" (Part One, Chapter
One), but he has also heard his voice in a dream. This phrase, "we shall meet in the
place where there is no darkness," has become a symbol of Winston's resistance against
the party. 

After a few minutes of conversation on the
topic of Newspeak, O'Brien gives Winston his address, on the premise that he can collect
the newest edition of the dictionary. In Winston's mind, this meeting had only one
purpose: "It had been contrived as a way of letting Winston know O'Brien's address." In
addition, it provides the proof to Winston that "the conspiracy he had dreamed of did
exist, and he had reached the outer edges of it."

While
there is no doubt that Winston will "sooner or later...obey O'Brien's summons," Winston
experiences a feeling of fear. This is because he knows that all rebels are found out
eventually, as the text says: "The last step was something that would happen in the
Ministry of Love. He had accepted it." Talking with O'Brien and taking the next step to
outward rebellion is akin to "stepping into the dampness of a grave." It is a scary
prospect which fills Winston with trepidation. 

It is a
tragic irony that Winston's sentiments in this scene foreshadow the events to come, long
before he ventures to O'Brien's apartment. But Winston is right to be concerned for his
future: he does, indeed, end up in the Ministry of Love and, even worse, in Room
101.