What does Winston write about the prostitute in his diary? Why does he write it?

Winston writes in his diary, revealing the details of a particularly sordid night when he had sex with a prole prostitute with a face thickly painted in makeup (which Party women never wear). Winston struggles with his internal turmoil surrounding this disdainful act. There was nothing pleasurable about it yet he feels compelled to write it down. He wants to purge the experience from his memory but it doesn't work. Perhaps, for Winston, a horrid feeling is better than feeling nothing at all.

In the diary, he tries to maintain some freedom of thought and express part of himself. Such recordings are an attempt to protest against state control over the personal lives and thoughts of citizens.