Crazy,Bitchy wife

Yes, it was a happy, and certainly a sexual marriage for the first several years. They were a beautiful couple, and married impulsively when they were both very young. Nobody really knows precisely how the marriage turned ugly, but it seems to have happened surprisingly suddenly after the birth of their last baby. The Duchesse wasn't a beauty anymore by the end (she'd put on some pounds over years of successive childbirth, and when things became emotionally strained it wore on her face and complexion), but the suddenness with which he started to repel her raises many unanswered questions.

Stanley Loomis' A Crime of Passion, the best account of the story I know of, suggests multiple hypotheses, as far reaching as the Duchesse being a potential lesbian or even that she committed incest with the children. None of this has been, or can be confirmed, and I doubt if the truth was anything so David Lynch-esque. But some contemporary documents suggest improprieties between the Duchess and one or two governesses, and the Duke's and his older daughters' letters refer cryptically to "infamies" between she and the male children. For whatever reason, he did see fit to restrict her interaction with the children.

I suspect that she was suffering a kind of post-partum depression that made her feel alienated from the children, and the lack of sympathy between them was perceived as repulsive and unwomanly by the Duke (who was influenced by idealized standards of femininity of the time). He stopped sleeping with her, she felt neglected, she compensated by suffocating him, and from there things escalated until they were completely out of control. Several of the ugly episodes in the movie seem lifted directly from the Duchesses desperate, imploring letters...others were far more dramatic in real life. On one occasion he went into her bedrooms and cooly, systematically crushed each of her parasols between his hands as she pleaded hysterically. Her mental issues go without saying, but frankly, the Duke's combination of coldness and cruelty come across as psychopathic through a modern lens. The nature of the crime, premeditated calculation coupled with violent rage, attest to that.