In 1984 how does Julia’s unwillingness to be separated from Winston, even to create a more successful rebellion, deepen her character and advance the plot?

Julia tells O’Brien she is willing to do any grisly task the Brotherhood asks of her in the name of the rebellion, except separate from Winston. Up until this point, her character seems to be a bit shallow, only rebelling just enough to please herself but not enough to create any meaningful change. She doesn’t really listen to Winston when he reads to her, because she really doesn’t want to work all that hard to resist the Party. She’s creative when it comes to finding a way to meet Winston, but it seems like this might be purely for sexual reasons. But when Julia says that the one thing she won’t do for the Brotherhood is leave Winston, the reader finally trusts that her love for Winston is real. Unfortunately, because O’Brien is actually a true member of the Party, this statement also provides the Party with leverage against Julia. They now know that to destroy her sense of humanity, the first thing O’Brien should do after arresting the two lovers is separate them.