Thouout Part one, he doubts the power of an individual to change Big Brother's regime and states that "If there is hope it lies in the proles" (60). But as he encounters the real Julia, a rebellious young woman, he refers their sex as "...a battle, the climax a victory. It was a blow against the Party. It was a political act." (105) This quote seems like Winston believes that the Outer Party can beat the system. Did he change his mind by meeting another person who is against Big Brother? I think he feels more comfortable now that he realizes he not alone because Julia did this "scores of times" (104). Winston is now more hopeful of the outer party and its secret corruption.
I think that Winston feels more comfortable performing the act of civil disobedience (sex with Julia) because she has done it before, but I don't think he feels the Outer Party can beat the system just yet or by himself. That would take a lot more than having sex with Julia. But his fervor for taking down the Party is increased after his time with Julia and that becomes obvious when he is invited to join the Brotherhood. He is willing to kill and even splash acid in children's faces in order to beat the system. I believe that (being invited to join the Brotherhood) is the point when he feels he has the best chance to take down the system.
I think, since his acquaintance with Julia, his courage to find others that are awakened like him grew. He even took it a step further and sucessfully joined the brotherhood by confessing his disloyalty to bib brother to an inner party member. I also think, after a couple of months living in this condition, he became too relaxed with it, and ultimately got caught.
I think that Winston feels detrimentally comfortable when with Julia - their relationship ultimately leads to his downfall. Winston takes thrill in the fact that Julia has had many sexual partners and is blinded by her rebellion. Beginning to experience a true life, Winston remembers what it's like to love. He grows as a target for the Thought Police as he takes the book from O'Brien and plans the destruction of the Party. He is finally caught. Yet, I don't think Winston would change what he had with Julia. He took comfort in feeling hopeful that there might one day be a way out. He took comfort in the mere fact that Julia was another person with which he could share his dreams.
I think he feels more comfortable now that he realizes he not alone because Julia did this "scores of times" (104). Winston is now more hopeful of the outer party and its secret corruption.