Well, this is a short one. I have a history exam this afternoon. About the lyrics- I think it means "The slow (about money, physically as in walking, maybe) boy is no longer my friend." Meaning the boy is "slow" about giving her back her money- the "shilling". Another thing, I think the prostitution thing is because of it could be a pun on labour as in work, and labour as in birth. Who would make someone give birth on a sofa? That's not to say that isn't probably correct that it's about pregnancy and having a baby, but "Make me lie on a sofa" kind of gives the impression that the narrator is being forced.