The Question and Answer section for 1984 is a great resource to ask questions, find answers, and discuss the novel.
I don't think that Winston ever believed in the brothorhood. Winston's only clear evidence is what O'Brien tells him about the brothorhood. Even when O'Brien tells Winston that it exists, there is something in Winston's intellect that knows the...
From the text:
The purpose of Newspeak was not only to provide a medium of expression for the world-view and mental habits proper to the devotees of Ingsoc, but to make all other modes of thought impossible.
Winston always wears the required blue overalls of the outer party members.