One would assume that a documentary about the legendary designer Yves Saint Laurent would be, ostensibly, about fashion. But "L'Amour Fou" begins with Saint Laurent's retirement from the fashion world in 2002.

It's the first signal that Pierre Thoretton's sometimes sluggish film won't delve deep into the realms of what made YSL some of the most recognizable initials in the world. Instead of haute couture, Thoretton focuses on Saint Laurent's relationship with Pierre Berge, his lover and business partner for 50 years. The film, the title of which translates to "crazy love," is meant to be more epic romance than a survey of Saint Laurent's career. But their love is not particularly crazy, despite the title, and "L'Amour Fou" sometimes trudges along with little insight into the genius of Saint Laurent.

Saint Laurent met Berge at the funeral of designer Christian Dior. The 20-year-old Saint Laurent was the successor to the Dior throne. When Saint Laurent was fired from the vaulted fashion house for avoiding his required service in the French-Algerian War, he enlisted Berge to help him start his own house. Their relationship lasted 50 years, facing different fashion fads and Saint Laurent's slow slide into depression.

Just as Thoretton begins his doc with Saint Laurent's end, he tells this love story through the auctioning off of Saint Laurent and Berge's extensive, and breathtaking, art collection. But the conceit is not established enough to tell Saint Laurent's story through what he owned, making the scenes of people boxing up Brancusis a tedious detour rather than insight into a complicated man. There are only so many close-ups of silver elephant statues that can be abided before the entire pace of the documentary is thrown off course.

Berge is Thoretton's main source, and it's fascinating to hear about the ascent of a man through the eyes of the man who loved him, especially one who got to see Saint Laurent evolve from the beginning of his career to his death at age 71 in 2008. Berge brings the camera into Saint Laurent's private spaces and exotic vacation homes that are decorated by a clear visionary of design, complete with walls covered in works by Goya, Warhol and, of course, Mondrian. (One of Saint Laurent's most famous collections appropriated the abstract painter's Composition works, reconstituting the rectangular themes into dresses.)

But it's also a one-sided portrait. Mentions of Saint Laurent's depression and drug use are fleeting and only scratch the surface.

Berge keeps his conversation to Saint Laurent, with a short respite to talk about his life in politics and AIDS activities. While Thoretton focused his lens on boxed-up artwork, he missed the real story right in front of his eyes.

Documentary produced by Hugues Charbonneau and Kristina Larsen, directed by Pierre Thoretton, music by Côme Aguiar, distributed by IFC.

There will be a discussion about Yves Saint Laurent with fashion-design professor Karen M. Karuza after tonight's 7:40 p.m. show.