In the course of Book 2, Chapter 5 of George Orwell's 1984, how and why does Winston change?

Book 2, Chapter 5 of 1984 in part
relates the story of Winston's 'summer of love'. Trysts with Julia in the bedroom above
Mr. Charrington's curio shop have worked astonishing changes in Winston's health: He has
lost the craving for synthetic gin. He has gained weight. The varicose ulcer on his
ankle, normally inflamed, has nearly disappeared while the coughing fits, which normally
doubled him over in the morning, have ended. A certain equanimity has entered his
emotional life: No longer must he fight the temptation to make faces at the telescreen,
or shout curses at the top of his lungs. With a place of refuge where a man can be a man
and a woman a woman, free from the artificiality and fraud necessary for existence in a
totalitarian world, Winston begins to taste what well-being, happiness, and freedom from
fear could be.