It is true that in the ninth chapter of part two Mick and Harry become closer in this chapter.  She and Harry have a conversation about Hitler, and fascism.  Harry and Mick have had to sacrifice things that were important to them and they are building a bond of mutual trust.  Mick decides that things are too serious and she begins to pretend to argue with Harry.  She pretends to start a fight.  They run into the ally and begin to wrestle.  The two of them struggle and then stop.  They look at each other in a new light.  Slightly embarrassed and confused they separate and go different directions.  They do not have sex here.  They do have a sexual relationship, but it is not at this point in the novel.