The Rococo discovered love amidst the garden statuary and embarkations for enchanted isles. The 19th century woke up the morning after. Working in a new art form, the novel, Dostoyevsky made it clear the party was over. The heroes of courtly art and legend had vanquished dragons and wooed damsels without having to contend with a guilty conscience. Crime and Punishment changed all that: most of the book takes place inside Raskolnikov’s feverish mind. In Dostoyevsky’s melancholy Notes from the Underground, it gradually dawns on a man and a woman, lying in the dark after making love, that they are total strangers. Art had discovered what it means to feel guilty. Edvard Munch made it his signature theme; Freud put psychosis on the map, duly crediting the Russian novelist.

In 1900, even Pierre Bonnard, the most sensual of painters, depicted himself in “Man and Woman” looking deeply troubled about the throes of passion. Marthe de Méligny, Bonnard’s muse and lifelong companion, was the defining obsession of his art. He painted her nearly 400 times. They met in Paris in 1893 when she was 16 years old. Thirty-two years later, when they finally married, Bonnard learned that her real name was Maria Boursin. Such are the mysteries of love.

Bonnard’s portraits of Marthe from the late 1890s are extremely intimate: Marthe asleep for an afternoon nap, stretched across the bed, nude, lying on her stomach, one foot bent over the other leg (“Siesta,” 1899); Marthe lying on the bed on her back, nude, again one foot bent, pressed up against the other knee, one arm behind her head, the other covering her breasts, her eyes locked with her lover’s just outside the canvas (“Indolence,” 1899). According to one of Bonnard’s friends, Marthe was like a little bird “with a tiptoe walk ... a timid air, a fondness for water and for bathing.” In Bonnard’s later paintings Marthe steps into or out of the bath or sits at her dressing table, always nude. She suffered from a skin condition relieved by the warmth of the bath water. But for Bonnard her skin was never blemished, she never aged, in his paintings she always remained the beautiful young woman of his desire.

Bonnard painted “Man and Woman” at the crossroads between the early Parisian interiors that established his career and his retreat to the secluded countryside. The man and woman are Bonnard and Marthe in their bedroom, moments after making love. She sits on the bed, her body dissolving in a hazy golden glow, stroking her cats, in no hurry to re-enter the hum of daily life. Bonnard stands moodily on the other side of a folding screen, in the darkness, head down, his brow knit, sunk in silent monologue. We have no idea what he is thinking. Is he hiding his guilt feelings after possessing the object of his desire?

In its strict separation into two parts, its contrasts between a man and a woman, the painting depicts a paradox. Sexuality represents a yearning to unite. The problem is, the word “sex” originates in a Latin verb that means “to cut off” or “sever.” It’s a sobering thought. The barrier is a revolving door. Standing alone in the shadows, Bonnard is certain of only one thing: The instant he moves around the screen and lays his eyes on Marthe’s lissome body, his desire will be rekindled, his guilt forgotten.

John T. Spike is on the faculty of the Masters in Sacred Art History organized by the European University in Rome and the Pontifical Athenaeum Regina Apostolorum.