In his lifetime, Winston's only experience romantically with a woman is his wife, Katherine, with whom he shared a rather boring and platonic relationship. They married but felt no real love for one another, and their physical relationship was a burden to her, something that she did not enjoy, did not participate in as an equal partner, and did out of "duty to the Party" as a way to produce children. It was a completely humiliating and unfulfilling relationship for Winston, and that is why they ended up separated. Any other interactions with women were, for Winston, similar: disappointing, and tinged with their Party-washed mind-views of Party duty, virtue, coldness and lack of passion. The Junior Anti-Sex League trained women to remain virtuous and to hate any form of intimacy. Julia hypothesizes that this was to control all passion that people might feel, and direct it towards passion for the Party, and country patriotism. She explains,
"the sex instinct created a world of its own which was outside the Party's control and which therefore had to be destroyed if possible. What was more important was that sexual privation induced hysteria, which was desirable because it could be transformed into war fever and leader worship."
So, love and sex were controlled and the passion and energy it creates is channelled into service towards the Party. If it wasn't done that way, it was too dangerous to the party because it created feelings it couldn't control, that were outside the realm of its power.
So, along comes Julia, a loving, passionate, rebellious woman who hates the Party as much as Winston does. She initiates contact, picks him out of the crowd, and gives him a wonderful, mutual relationship that is fulfilling on every level from physical to emotional to mental. There is no wonder that Winston fell for her--she fulfilled him and made him happy. She loved being with him, and matched his passion physically and emotionally. I hope that those thoughts helped; good luck1
Winston falls in love with Julia because she represents something to him, not really because of who she is. Winston hates the Party more than anything and what he wants to do is to hurt the Party.
When he finds out that Julia hates the Party too, that really attracts him to her. He doesn't really care why she hates the Party, but so long as she does, that is fine with him. So he's in love with her because she hates the Party.
As far as your second question, I will include a link below -- this question has been asked before.