Julia tells Winston that their next meeting is going to have to wait. She happened to be experiencing her time of the month. At first Winston gets entirely upset at her, but then,
...just at this moment the crowd pressed them together and their hands accidentally met. She gave the tips of his fingers a quick squeeze that seemed to invite not desire but affection.
Prior to this moment, their joining together had been about pure sex. Now, Winston is realizing that he actually longed for something more than just a physical experience. He wanted the long-term relationship, the companionship, and the developing of a household together with a woman. These aspects of human nature were so foreign to him that he did not realize he had the capacity to feel this way. That simple touch of affection among all of the other people made Winston feel this intense tenderness to Julia.