It’s a volatile combination for a couple: One man is addicted to love, the other to crack cocaine.

That’s the basis of the impressive "Keep the Lights On," a harsh yet delicate tale of two New Yorkers whose codependent relationship is fueled by sex, drugs and complex longings for companionship.

The story, which spans almost a decade, starts out in 1998 as young professionals Erik (Thure Lindhartdt) and Paul (Zachary Booth) hook up after a phone sex chat. Paul soon extricates himself from his girlfriend, but not his crack habit. The lonely Erik quickly finds himself in too deep to turn back.

Director Ira Sachs, employing gifted cinematographer Thimios Bakatakis ("Dogtooth"), opts for a grainy yet beautiful palette to tell this impressionistic story, which parachutes in at random moments during the relationship.

‘KEEP THE LIGHTS ON’ Not rated Now playing at Consolidated Kahala

The film is at its best in the bedroom, not shying away from the sexual relationship, but not sensationalizing it, either. There is great sex, clumsy sex, tender sex — and it’s all crucial to the story. Such genuine intimacy, whether gay or straight, is virtually nonexistent in American cinema. It’s enthralling to see it here.

The strongest moment in the movie occurs when Erik returns from a successful business trip in Berlin and finds Paul on another crack binge. Sachs wisely underplays the moment, making the scene all the more real and memorable.

Indeed, the director (who launched his career with the hypnotic and underrated "The Delta") astutely avoids melodrama and bathes his film with a gentle but lush score from the late cellist Arthur Russell (another wise choice).

The only problem here is that the story doesn’t build. It never gets boring, but it doesn’t go much anywhere, either. That was probably intentional, but the final minutes don’t carry enough power, and although "Keep the Lights On" deftly explores the codependent and addictive elements of the relationship, other aspects of these characters are less drawn, leaving the actors adrift at times.

Overall, though, this is accomplished work. It’s clearly a personal story, and it’s a marvel how Sachs straddles the line between delicate and harrowing for the entire film.