The central dramatic element in The Swell Season, a nicely captured black-and-white doc about how Glen Hansard and Marketa Irglova coped with the success of Once, is, of course, the breakup of their romantic relationship. And the big torpedo, boiled down, is Irglova’s inability to deal with the hooplah, which is due to her being too young.

This is almost completely typical. Whenever an under-25 performer suddenly hits it big, they tend to withdraw from the resulting attention, and then rebel against it in this or that way. Leonardo DiCaprio seemed to more or less freak out in the wake of Titanic‘s success, and didn’t really ease back into things until two or three years later. So the 20 year-old Irglova being unable to roll with being a sudden “star” fits right into this.

Hansard, on the other hand, is totally cool with backstage admirers, and gradually starts shaking his head at Irglova’s hissy fits. And you can see where it’s all heading.

So what the film boils down to is a portrait of a once-beautiful relationship (as depicted in Once, at least) that was probably doomed to start because of age disparity. Hansard is now 41; Irglova was 19 when Once was made, and 20 when the big success happened. They were toast as of 2009. Irglova got married last June to Tim Iseler, a studio engineer.

Otherwise the doc, co-directed by Nick August-Perna, Chris Dapkins and Carlo Mirabella-Davis, is an engrossing portrait of the musical performing world, and is very nicely captured in black-and-white.