“My Golden Days (Trois souvenirs de ma jeunesse),” a devastating romance from French writer-director Arnaud Desplechin, unreels in three distinct, unequal acts. Part one recounts the tortured, tragic childhood of Paul Dédalus. Act two details a daring act of youthful courage.

The obligatory first act provides necessary foundation for Paul as a young and middle-aged man. The superfluous second act features a risky visit to Russia during which Paul and a friend help Jews escape to Israel.

Patience is tested during the first two acts of Cannes Film Festival favorite “My Golden Days,” which opens the French Film Festival on Thursday at the Orpheum Theater. And then Desplechin launches his emotion- and conflict-mined third act.

The movie’s pièce de résistance, act three makes “My Golden Days” a masterpiece of modern French cinema. It’s enthralling while it’s on the screen and haunting in post-screening aftermath.

A brief prelude introduces Dédalus in middle-age. An anthropologist who’s lived throughout the world, he’s preparing to return to France following years in the former Soviet republic of Tajikistan.

Matheiu Amalric plays Paul, a man whose presumably last moments with the girlfriend he’s leaving in Tajikistan is nothing more than a pleasurable, casual sexual encounter. No flaring emotions. Save them for later.

Quentin Dolmaire plays Paul as a young man. Earnest and scholarly though he is, Paul can also be light and playful. Dolmaire’s acutely focused performance, spanning many moods, emotions and experiences, is strong enough to qualify him as an exceptional young talent.

Paul’s significant other in the story, Esther, is the alluring girl coveted by everyone in Roubaix, their hometown. Lou Roy-Lecollinet, previously seen in the lesbian romance “Blue is the Warmest Color,” is enchanting and enigmatic in “My Golden Days.” Roy-Lecollinet’s provincial goddess already is an old pro at effortlessly breaking boys’ hearts. The actress handles the character’s bravura and casual cruelty with natural ease.

Desplechin introduces Esther during an ensemble scene that may achieve classic status. The director places Esther on an actual pedestal. Set at the center of everything, she displays herself where she can’t be missed.

Paul, like every other young male, is drawn to this magnetic creature. Despite the slim chances of winning Esther, his nimble, self-deprecating flirtation entertains goddess and moviegoer alike.

Befitting her town beauty rank, Esther won’t be easy.

After Paul invites Esther to a party at his family’s house, she arrives with a guy in tow. Paul is confused and humiliated. Maybe it’s just a game? Watchful Paul decides to play. At the party, Dolmaire, working with Desplechin’s clear, assured direction, beams the mostly silent Paul’s puzzlement and calculation.

The relationship between Paul and Esther, played in devastating strokes by both actors, quickly grows into the sweet and challenging love of a lifetime. Well, for Paul at least. Esther never completely loses her mystery, even though the vulnerability beneath this haughty beauty eventually surfaces.

The joys and sorrows they share unravel in mesmerizing style. They experience life’s greatest fulfillment — and its greatest disappointment, expressed passionately by Amalric as the middle-aged Paul.

The movie’s enigmatic ending leaves a door open for interpretation. Nonetheless, it’s Paul’s anxious state of mind and inconsolable frustration that linger after the film’s final credits. Desplechin’s unforgiving portrait of Paul and Esther, in intense love and distress, is difficult to shake.