With “Passages,” American indie darling Ira Sachs (“Love Is Strange”) makes his first film in France, a brutally honest portrait of a train-wreck relationship in which an openly gay director sabotages his marriage — and maybe his life — by falling for a woman. Affairs happen; that’s nothing new. But this one proves unusually destructive, giving three stellar international actors — German actor Franz Rogowski (“Great Freedom”), Ben Whishaw (“The Lobster”) and Adèle Exarchopoulos (“Blue Is the Warmest Color”) — a chance to tear one another’s hearts to shreds. Domestic interest will be limited, as it always is with Sachs’ shoestring heart-tuggers, but having his previous movie, “Frankie,” selected for Cannes should give “Passages” a certain entrée in Europe.

Like a less-tyrannical, latter-day Fassbinder, queer auteur Tomas (Rogowski) is used to calling the shots. On set, the cast and crew put up with his tantrums. At home, longtime partner Martin (Whishaw) humors his needy husband’s caprices. But this time, Tomas may have gone too far, hooking up with Agathe (Exarchopoulos) after the wrap party for his latest film, and the subsequent implosion is something to witness, like watching a toxic supernova collapsing in on itself. In Paris. Which is by far the sexiest place for romance to unravel.

“You could say that you’re happy for me,” Tomas challenges Martin after confessing the affair, making the transgression about himself, as he does most things. Tomas is more than a mere narcissist; he’s a borderline sociopath, lying and manipulating to get what he wants, and Sachs’ latest warts-and-all relationship study — a fitting companion piece to 2012’s blisteringly personal “Keep the Lights On,” also co-written by Mauricio Zacharias — observes the trail of destruction that such a personality leaves in his wake.

Whose side is Sachs on? There’s no question that he feels for Martin, a slightly co-dependent enabler who’s clearly been humiliated by Tomas before. Sachs also empathizes with Agathe, the young woman who’s drawn to Tomas’ fame as well as the idea that she may have seduced a gay man, but sincerely wants to think that this one-night stand could have a future. Sachs even feels a certain amount of pity for Tomas, in whom the helmer may see a certain amount of himself. Incorrigible as the character may be, Rogowski is too complex an actor to turn Tomas into some kind of monster. In fact, his costumes — eyesore sweaters and situation-inappropriate crop tops — suggest more of a clown at times.

Sachs excels at investigating thorny, uncomfortable situations, and he treats all three characters fairly here, which allows audiences to decide which one they identify with. It should be said: Despite superficial similarities to the hit play “Cock,” the movie is not a serious portrait of bisexuality. However, its depiction of a difficult and self-absorbed artist chimes with recent criticisms of industry misbehavior — how power and celebrity bring a kind of entitlement — which gives the movie added cachet.

“This always happens when you finish a film. You just forget,” Martin tells Tomas. That line captures the shrewd, soul-piercing quality we’ve come to expect from Sachs and Zacharias, who’ve now collaborated on five films together, resulting in the richest stretch of the director’s career. Instead of serving up a playlist of all the obvious high-drama scenes we think we want from a love-triangle movie, they’re just as likely to portray the quiet, in-between moments, planting clues that allude to arguments and arrangements that occurred when the cameras weren’t eavesdropping, but which intelligent audiences can infer.

“Don’t be melodramatic,” Tomas chides Martin when the latter dares to call him on one of his lies. Yet that could easily be the film’s mantra, as Sachs dedicates himself to steering clear of clichés without sacrificing truth. For all the raw emotional realism the director brings to his work, there’s always been a certain clumsiness in the way he stages a scene. But each film brings him closer to his European art-house idols: Eric Rohmer, Maurice Pialat and, perhaps most relevant here, Jean Eustache. At times, “Passages” plays like a queer riff on Eustache’s landmark “The Mother and the Whore,” about a bourgeois twentysomething torn between two lovers who, instead of deciding, tries to force them into cohabitating.

After Tomas takes his things and moves in with Agathe, Martin rather briskly rebounds with an up-and-coming French novelist, Amad (Erwan Kepoa Falé). He knows the relationship will make Tomas jealous, and it does. The thing with narcissists is that they can be exasperatingly predictable. As if on cue, Tomas is back, having make-up sex with Martin. Sachs isn’t the slightest bit shy about showing audiences what passion looks (or sounds) like between his characters, though this particular session goes on a little long and might have played better on their faces.

What happens next, no one saw coming, and rather than spoil it, suffice to say that Tomas’ self-absorption reaches new heights in the strategy he uses to suggest a ménage à trois — not a threesome, mind you, but a new domestic arrangement in which he can be surrounded by the two loves of his life, both of whom take a back seat to his ego. The movie argues that directors are called upon to be selfish, dictatorial jerks, in order to make great work, which might encourage such misconduct. But in the end, it’s Tomas who winds up being the melodramatic one, staging an over-the-top take-me-back scene that might have worked in some cornball Hollywood movie. Since Sachs’ films feel as if they were ripped from real life, however, this is one situation he can’t control.