After dinner, Jem Harthouse takes Tom back to his hotel, and handing him a drink and a cigar, converses with him as a guise to extract information from him about Louisa. He learns that Louisa married Bounderby not out of love but for Tom's sake, to help him advance and to ensure that she could help him out financially given his frequent money troubles. Tom adds that Louisa would probably do anything for him, a point upon which Tom displays some satisfaction.
Tom is utterly insensitive to his sister's feelings and the nature of the private information he is revealing to a total stranger. He seems to care only about what he can get for himself without actually working for it.
Tom stumbles home at the end of all this talk, drink, and smoke, and the narrator darkly hints that the night's conversation will have dire consequences on all parties involved.
Mr. Gradgrind's education of facts has indeed prepared Tom poorly for all the pleasures open to young men of his status. The narrator's comment after Harthouse's interest in Louisa's lack of love with Bounderby forebodes that Harthouse will see this as an opportunity to gain her love. It is worth noting here that this would have been a much bigger deal in Victorian England when the novel was written than it would today. In Victorian England, a woman who had an affair would be ruined, shunned by society.