It is clear that by the time Winston is released back into mainstream society he has lost all feeling for Julia, and she has also undergone a similiar negative transformation. This is something they had both never believed possible before their arrest.
"'They can't get inside you,' she had said. But they could get inside you."(p.303)
The passion Winston once felt for Julia has been extinguished under the extreme psychological torture that O'Brien exposed Winston to in Room 101. The profound sense of shame that Winston feels afer the event means that he cannot recapture the feelings he once had for Julia. This is shown in their chance meeting at a park where we learn that Julia was evidently exposed to an identical psychological torture.
"'I betrayed you,' she said baldly. 'I betrayed you,' he said" (p.305)
The circumstances O'Brien created for Winston to lose his feelings for Julia (and vice-versa) were more than adverse, they were extreme, but he knew that he must break down their bond if he was to truly succeed in redirecting their love and loyalty towards Big Brother.
In Part Two, Chapter Two of 1984, Winston meets with Julia for the first time, and he thinks to himself that true love cannot exist under the Party because "you could not have pure love or pure lust nowadays. No emotion was pure, because everything was mixed up with fear and hatred."
In other words, since the Party came to power, it is not possible to feel the same emotions as before. Through propaganda and control techniques, like the telescreens, the Party has manipulated people in loving only Big Brother and, even if they do not truly feel love for him, they are too terrified to ever admit, or even think, it.
Arguably, for Winston, being with Julia is as much about politics as love. It provides him with an opportunity to rebel against the Party by exerting his own will and creating a loyalty with her, instead of Big Brother. As such, it is possible that Winston never really loved Julia. This is significant in itself because this represents Orwell's key message that totalitarianism is the enemy of love and other emotions. It is for this reason, among many others, that such political regimes are dangerous and must always be overcome.