Winston satiates that the rendezvous with the girl was a political act. What does he mean by this statement?

Winston is alluding to the fact that his relationship with Julia is as much a political statement and act of rebellion, as it is anything else. 

Evidence of corruption and abandon always gives him with hope. Perhaps the whole system is rotten and will simply crumble to pieces one day. The more men she has had, the more he loves her, and later as he looks at her sleeping body, he thinks that now even sex is a political act, a blow against the falseness of the Party.