Susanna Fogel's Life Partners starts with a vehicular meet-cute: Paige (Gillian Jacobs) cuts off Sasha (Leighton Meester), causing the latter, an aggrieved receptionist/wannabe rock star, to scream, “Watch where you're going, bitch!” Both girls park at a gay-pride rally, storm out of their cars and hug. It's a fake fight — the old school friends bond by bellowing “slut!” — and the sort of inside joke that sets the tone for an upside-down romantic comedy where the centerpiece love story is platonic.

Paige and Sasha are bourgeois soul mates; they genuinely prioritize each other's happiness, even remembering which pillow the other prefers when crashing on the couch after too much rosé. “I just want to meet a guy that I like as much as you,” Paige sighs, and from the way Jacobs and Meester grin at each other, we get that their chemistry is impossible to duplicate.

Their lovers — men for Paige, ladies for Sasha — come second, until one day one of them doesn't. (Sasha's lesbianism is no more important a distinction than whether she's a blond or a brunette.) That Paige's serious boyfriend is a dorky dermatologist named Tim (Adam Brody) who quotes Will Ferrell flicks as if they're the height of humor is as mystifying to us as it is to the suddenly shafted Sasha. This guy? Really?

Though the ladies are determined to be BFFs for life, the interloping dweeb reflects their friendship like a funhouse mirror. To Sasha, Tim represents Paige's closeted conventionality — around him, she's quieter, more buttoned-up and bourgeois. To Paige, Sasha's insistence on dating young hotties who still live with their parents proves that she's pathetically refusing to mature.

In turn, as both are 29-going-on-actual-adulthood, the lifestyle differences that once felt trivial, like Paige's burgeoning law career versus Sasha's dead-end receptionist job, feel increasingly irreconcilable.

These sound like broad brushstrokes, yet Fogel and Joni Lefkowitz's script captures the girls' relationship in fine detail. It's fated they'll clash — every rom-com needs a massive fight before the happy ending — but Life Partners wrings its drama from how hard both Paige and Sasha sweat to stay close. Meester and Jacobs show us the strain even when the friends seem fine on the surface: They laugh a little too hard, smile a little too tightly, make jokes that land as weakly as pennies in a dry well. It's a no-fault separation, and what the film cedes in laughs, it makes up for in honesty — down to the awkwardness of our realizing, too, that neither of them will ever date anyone she likes as much as the other. (Maybe the best they, or anyone, can do is deal with the slight disappointment of accepting that you'd rather be sharing the TV remote with your best friend.)

Here, change is inevitable — even change that makes life less fun. Fogel refuses to pander by pretending that the girls can fix everything with a hug. Sacrifices must be made. Still, Life Partners admits that we are who we love, that the people we choose to be by our side are the truest portraits of ourselves, no matter if we're wedding them forever or spending every Wednesday gossiping over reality TV.

LIFE PARTNERS | Directed by Susanna Fogel | Written by Fogel and Joni Lefkowitz | Magnolia Pictures | On demand

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