Ira Sachs’ deceptively casual “Passages” offers a glimpse into a rich relationship.

Sex scenes in cinema are often offered up as passing diversions, as titillating breaks between the blocks of real narrative. The possibility for sexual scenes to continue a story, or be the story itself, is still relatively unplumbed, especially in our modern cinematic era in which we pretend that sex doesn’t exist. However, Ira Sachs’ “Passages” is a bracing disruption of this trend. Sachs dramatizes a romantic triangle verbally, unleashing some of the sharpest dialogue of the year, and physically, as the couplings reveal vulnerabilities, shifts in power, and of course erotic yearnings.

“Passages” opens on a film set in Paris, as Tomas (Franz Rogowski) directs an actor on how to descend a stairway into a club. Tomas isn’t satisfied with the energy the actor is transmitting in the seemingly simple action. The actor is fraught and dramatic, while Tomas is asking for an impression of effortlessness, of fun and belonging. As directed by Sachs, this scene is more than a perfunctory acknowledgement of Tomas’ work; instead, we see the practical negotiations between director and actor and the details that tend to interest filmmakers with strong senses of style. The descension of the stairway is also, pardon me, a moment of passage—a moment that Tomas is staging as a reflection of the transitory moments between locations and mental states that define our lives.

Another transitory moment follows. After filming, Tomas meets his husband, Martin (Ben Whishaw), at a bar. Keyed-up from filming, Tomas is itching to party while Martin is ready to leave. After Martin’s departure, Tomas meets Agathe (Adèle Exarchopoulos) and they dance. This moment—so realistic and seemingly tossed-off—is among the sexiest dance sequences in cinema. Sachs renders the initiation of a hook-up in entirely physical gestures, showing Tomas’ come-on, Agathe’s hesitation and engagement, as well as their evolving physical unity as they gradually move in sync. Sachs achieves the quality that Tomas desires in his own film—creating scenes rich in sensual vibes and atmospheres that speak for themselves—without the contrived burden of over-emphasis, particularly the crutch of expositional dialogue. Remarkably, Sachs maintains this paradoxical sense of clarity and mystery for the entirety of the film’s 91 minutes.

Tomas and Agathe sleep together—in a moment of frenzy that’s also vivid and emotionally realistic and all the more sensual for it—and Tomas goes home to Martin the next morning and tells his husband about it. At least two impressions arise: Tomas’ matter-of-factness with his announcement of getting laid suggests that they have an open relationship, though Martin is … what is Martin? Throughout “Passages,” Whishaw and Sachs inform this character with a wealth of contradictory nuances that suggest a real person rather than someone invented by artists. Martin is upset, which he attempts to transmit as mere irritation. Is he upset because sex with a woman, which appears to be new to Tomas, constitutes a violation of their arrangement? Or is he manageably-mad about Tomas being out all night? Or is Martin, and this I think this might cut closer to the truth, tired of pretending that he’s too hip for fidelity and, by extension, exhausted with indulging Tomas’ wild hairs, sexual and otherwise? It is unusual to encounter this kind of emotional suggestiveness in popular movies, which tend to be allergic to subtext at all, much less in numerous, conflicting forms.

Tomas becomes torn between Martin and Agathe and yet Sachs never drums up this conflict as familiar melodrama. Everyone is so matter-of-fact and well-defended. The deceptively casual tone—for much is at emotional stake here—that Sachs maintains is more reminiscent of European than American films. Tomas, the disruptor, is actually the least defended. He’s a raw nerve, constantly needing to move, to transition from one moment or scene to another—he’s a primal, uninhibited, immature man bridled by relentless restlessness. Martin implies that these romantic confusions might even be routine for Tomas in the aftermath of finishing a film, and Martin’s own behavior suggests a kind of role play—he’s accustomed to being a sane sounding board for Tomas and he both gets off on this role and is fed up with it. They are the kind of opposites that one encounters in couples in real life: the impractical creative and the person who ensures that the trains run on time. That 91-minute running time is crucial to this film’s culminative effect: “Passages” is suggestive, roaming yet fiercely honed. You feel as if you are seeing but a glimpse of a rich relationship.

It is characteristic of Sachs’ allergy to cliches and simple conflicts that Tomas and Martin continue to sleep together even after Tomas leaves Martin for Agathe. Their relationship, in the wake of its brief, perhaps routinized destruction, is physicalized in a long and detailed sex scene, the scene that certainly earned “Passages” its NC-17 rating. Martin is dominant, and we see the men from a fixed angle: Martin’s back is to us while he penetrates Tomas in a missionary position. This isn’t a sentimentalized, gauzy love scene. It is about two men getting off. It is about Martin, who seems so controlled, so resigned, so roll-with-the-punches, allowing his steeliness to rise to the surface; while Tomas, who tends to dominate social situations, allows his submissiveness to bloom—a side that he does not show to Agathe. This scene treats us like adults, showing how Tomas and Martin’s relationship is writ physically, both expressing and further burying their tensions as a couple.

Rogowski, who has been coming on strong lately in films like “Transit” and “Great Freedom,” is every bit as moving and singular as Whishaw. He gives Tomas’ flakiness an agonizing force that can, at times, be as oddly funny as it is poignant. Exarchopoulos has the potentially thankless role as the new person stuck between two huge personalities who serve as one another’s North Star. Sachs pays nearly as much attention to Exarchopoulos as he does his leads, and she flourishes in her most notable role since “Blue is the Warmest Color,” giving Agathe a subtle, tender streak of self-loathing.

WhileTomas may be the nucleus of “Passages,” its most powerful scene belongs to Martin and Agathe. Life has conspired to break their hearts, most prominently for denying Martin from being further cuckolded, and this moment of unexpected communion between ostensible rivals epitomizes how damn tough this wonderful movie is. The title of another Sachs film has it right: Love is strange.

“Passages” is available to stream on Mubi beginning Aug. 4.