Valmont has at long last accomplished his mission. Having gained access to the Présidente de Tourvel's house through her priest, he has met and slept with her. He reports this joyous news to the Marquise de Merteuil in Letter One Hundred and Twenty-five, along with the news that Prévan, in addition to being imprisoned, has been forced to leave his regiment following the scandal with Merteuil.
Letter One Hundred and Twenty-six, from Madame de Rosemonde to Tourvel, maintains their relationship as mother and daughter and adds to Rosemonde's list of roles that of doctor. She says that she will care for Tourvel during this difficult time, as she learns to resist her love for Valmont.
In Letter One Hundred and Twenty-seven, the Marquise de Merteuil expresses her disdain for the Vicomte de Valmont's suggestion that they get back together in no uncertain terms. She describes how such a reunion would be disadvantageous to them both, requiring each to make too many sacrifices to the other.
The Présidente de Tourvel confesses to Madame de Rosemonde all that has transpired between her and Valmont (Letter One Hundred and Twenty-eight). She tells her that he now rules her life, and that just as she is entirely devoted to him, so has she entirely accepted her own ruin.
Valmont tries to smooth things over with the Marquise in his next letter (Letter One Hundred and Twenty-nine). He tells her that there is no woman in the world he prefers to her, and that his habit of flattering Tourvel and Cécile in the letters he writes is just his manner of speaking.
Madame de Rosemonde attempts to comfort Tourvel in Letter One Hundred and Thirty by telling her that she is far too good to be loved as fully as she deserves or ever to be happy in love. Rosemonde also speculates on the difference between men and women: women take pleasure from giving love and men from taking.
The Marquise de Merteuil, meanwhile, accepts Valmont's apologies and protestations (Letter One Hundred and Thirty-one). She remains skeptical, however, about whether they can be happy together again.
Tourvel replies to Rosemonde (Letter One Hundred and Thirty-two) to tell her that she is now thoroughly debauched and also thoroughly happy. It is a strange and sinful combination, and as such, she will trouble Rosemonde no more by writing to her of it.
Valmont promises the Marquise that he is not in love with Tourvel in Letter One Hundred and Thirty-three and swears that he will soon send her proof of his affair with the Présidente. But the Marquise is not so easily satisfied. In Letter One Hundred and Thirty-four, she accuses him of being in love with Tourvel and hiding it from himself. She suggests that they just be friends in the future, since Valmont's lingering feelings for the Présidente would get in the way of anything more. She also announces that she has now entirely ended her affair with the Chevalier de Belleroche.
Indeed, Valmont has ended his affair with Tourvel very suddenly. The Présidente writes to Madame de Rosemonde (Letter One Hundred and Thirty- five) to tell her the sad news: Valmont left Tourvel without warning at home, and she later saw him with a prostitute. The Présidente then writes to Valmont (Letter One Hundred and Thirty-six) to tell him never to darken her doorstep again and to ask him to return her letters.
Valmont replies (Letter One Hundred and Thirty-seven) to tell Tourvel that appearances have deceived her. He begs her not to end their affair so suddenly.
In this exchange, the theme of illness and doctors and the comparison of love to an illness appears for the first time. The Présidente de Tourvel is in correspondence with Madame de Rosemonde, whose rheumatism often prevents her from writing her own letters. Madame de Rosemonde writes (Letter One Hundred and Twenty-six) that, ill as she is, she herself will serve as Tourvel's "doctor" ("Médecin") during this period of grief over love. It is interesting that Rosemonde does not offer herself up as confessor or comforter, and that the suggestion that love is a sickness proves so convincing—soon Tourvel will indeed die of love for Valmont. What he sought to describe as a kind of religious devotion or sacrifice, Madame de Rosemonde wishes Tourvel to view as an "indisposition." Illness can be cured, but one must devote oneself to one's religion without the hope of return.
But the Présidente de Tourvel's devotion to Valmont is religious in nature. She might as well have decided to become a nun. As "the sole center of her thoughts," Valmont guides Tourvel's life like a divinity. His subjugation of religious themes to his own convenience, and his subjugation of Tourvel, is now complete.
There is also much meditation on the roles of the sexes and the nature of love. In fact, the divergent roles of the sexes seem to be defined by their differing reactions to love. Madame de Rosemonde has a very simple definition in Letter One Hundred and Thirty. Indeed, the Marquise de Merteuil seems to agree with Madame de Rosemonde on the absolute difference between the two sexes, for she writes to Valmont (letter 131), "Have you not observed that pleasure, which is undeniably the sole motive force behind the union of the sexes, is nevertheless not enough to form a bond between them?" (Le plaisir, qui est bien en effet l'unique mobile de la réunion des deux sexes, ne suffit pourtant pas pour former une liaison entre eux....) The difference between the sexes is not in question in Dangerous Liaisons: the only question is where, and how, this difference lies.