Dakota Fanning in Joe Swanberg Dramedy

“Zero part of me wants to do what I’m doing right now,” insists Jack (Jake Johnson) as he prepares to tell Wendy (Dakota Fanning), his girlfriend of two years, that he thinks they should take a six-month break. He believes she needs the space to figure out what she wants, even as she pleads that what she wants is him.

Oddly, he seems to mean it, or at least to believe he does. He really is happy with her; he really doesn’t have an ulterior motive; he really does intend to just sit around for the next six months, waiting to see if she returns.

Why, then, he mounts this ultimatum anyway is one of the emotional mysteries of The Sun Never Sets. Mostly they’re fun ones, thanks to writer-director Joe Swanberg’s knack for naturalistic chemistry and eye for casual beauty. But just as listening to a friend dither over an on-again, off-again relationship gets old eventually, there’s a limit to how many times Jack and Wendy can flip and flop before the beats grow repetitive.

Initially, Jack’s edict has Wendy reeling. It’s true that she’d always thought she would get married and have kids, and that Jack, who’s a bit older, has made it clear he has no intention of getting remarried or having more kids. But she’s made her peace with the compromise, doting on Jack’s adorable children with his first wife (Anna Konkle) without a trace of resentment. Never mind that her best friend (Debby Ryan) announcing she’s pregnant sends Wendy screaming to herself in her car, overwhelmed to see everyone else moving on while she feels stuck in place.

But then Wendy runs into Chuck (Cory Michael Smith), the ex who got away. Suddenly, Jack’s out-of-the-blue demand looks like a blessing in disguise — especially since this Chuck claims he’s ready for commitment and a family, in contrast to the “scared little bitch” he freely admits he was three years ago. And suddenly, Jack is forced to confront the possibility that his little experiment might not go as planned.

From there, Wendy ping-pongs between the family-man boyfriend who’s not really her boyfriend at the moment, and the fuckboy former flame who’s no longer quite so former. The men oscillate between wooing her and disappointing her, sometimes to comic effect and sometimes to a more bittersweet one. At every turn, all three struggle to distinguish between what they want, what they want to want and what they don’t actually want but are just afraid of not having.

Swanberg’s loose approach to storytelling, in which he outlines a plot and then lets his cast improvise the lines, is perhaps the movie’s greatest asset. Even when the plot machinations feel engineered, as they tend to when characters change their minds as frequently and vehemently as these three do, the cast’s warm, comfortable chemistry — built through body language, shared looks and off-the-cuff remarks — keeps their feelings grounded in a believable spontaneity.

Johnson (whose previous collaborations with the filmmaker include the exceptionally astute Drinking Buddies) is particularly adept at this style of performance. He brings to Jack a playful self-awareness, which paradoxically makes him easier to buy as a real person: Where a fictional one might react to soap operatics like an argument in a bar bathroom with tears or screams, Jack starts laughing, able to see the absurdity of the situation for what it is. This sense of humor, in turn, makes him easier to root for even when he acts, every so often, like a petulant brat.

Fanning, who has rarely looked more radiant despite Wendy spending most of her time in sensible workwear and minimal makeup, has strong enough chemistry with both her leading men that we can see why she’s torn between them, as well as enough magnetism of her own that we want her to be happy even when her behavior tips toward self-sabotage. And Smith is effectively alluring as Chuck, though his is the least developed corner of this love triangle. He’s a hunky symbol for Wendy and Jack to fight about rather than a protagonist with his own legible motives and desires.

That all of this endless will-they-won’t-they is playing out against the natural splendor of Anchorage’s endless summer days (captured in 35mm by cinematographer Eon Mora) and gorgeously sunlit blond wood interiors (staged by production Aaron Bailey) makes it go down quite easily for a while. If nothing else, The Sun Never Sets mounts an excellent case for visiting Alaska and possibly looking for love there — even if slightly snobbish mainland transplant Jack does describe the local dating pool as “a bunch of goofy guys who smell like salmon.”

If the setting is beautiful and the characters vivid, however, the path that the film cuts through them ultimately proves too jerky and repetitive to take us anywhere truly illuminating. It’s true enough that our heart’s desires can be a puzzle even to ourselves, and that solving it can be the work of a lifetime. But there’s a difference between a character who doesn’t know what to make of themselves, and a film that doesn’t quite seem to know what to make of them either.