Winston tells Julia that the greatest betrayal is one that comes from the heart rather than the mouth.

As they lie together in their secret room in Part II, Chapter 7, Winston thinks about his mother and the unconquerable love that she possessed. Even when his little sister was so weak that her survival was impossible, his mother clutched the child to her and tried to protect her. What she felt for her child never ended.

When Julia points out that nearly everyone eventually confesses because people cannot stand the pain and torture that they are put through, Winston explains,

"I don’t mean confessing. Confession is not betrayal. What you say or do doesn’t matter: only feelings matter. If they could make me stop loving you—that would be the real betrayal."

Julia counters, declaring that no one can alter a person's deep feelings. Winston contemplates what she says, especially as he thinks back about his mother's undying love for his sister. Again, he returns to thoughts of his mother, whose feelings for her child were unalterable. Such feelings of the heart, Winston concludes, remain "impregnable."   

Winston tells Julie that the real betrayal will be if the Party could make them actually stop loving one another.  They both realize that, under duress, they will inevitably confess their forbidden love, because, as Julie observes, "everybody always confesses.  You can't help it.  They torture you".  Wilson, however, says, "Confession is not betrayal.  What you say or do doesn't matter; only feelings matter.  If they could make me stop loving you - that would be the real betrayal". 

After thinking about it, Julia concurs that "they can make you say anything...but they can't make you believe it".  Both Winston and Julie agree that although the Party may be able to control their actions, they cannot control their feelings; "they can't get inside you".  Sadly, as events will show, Winston and Julia severely underestimate the power of the Party (Part 2, Chapter 7).