There’s a certain sense of openness, of frank honesty, which one only really gets with an ex-lover. When the conversation hangs between twin points of nothing to lose and nothing to gain, that’s when all the truth can come out.

In her immensely affecting and very cool debut Miss Ex, Jeong Ga-Young pirouettes between those points with a humour and charm which belies a promising future for this young Korean director.

It’s tough, being young. I realise that this isn’t a shockingly original insight, but it’s worth repeating every now and again. Recent news that record numbers of teenage girls suffer from depression has – rather than inspiring renewed investment in early stage mental health care or more sensitive involvement by parents in their children’s lives – prompted a fresh wave of righteous condemnation of social media, the internet and smartphones.

Don’t get me wrong, the internet is terrible and social media is making our lives markedly worse. But there is something about the very fact of being young, those first tottering steps toward self-acceptance, which is infused with a melancholy all too easily forgotten once you have to deal with adult miseries like money and other people.

Perhaps the most arresting aspect of this highly likeable film is its understanding of this complex simplicity of youth. Miss Ex takes place almost entirely within the apartment of Jeonghoon’s (Kim-Choi Yong-joon) absent parents. The young Jeonghoon is idly watching The Dark Knight when his ex-girlfriend Ga-young (played by the director) shows up drunk, spoils the ending and then proceeds to hijack his day. In the inimitable (although here, obviously, expertly imitated) way of the aimless young they discuss life, movies and each other in a way which is both intimate and engaging, even through the middleman of subtitles.

Often in films which restrict themselves for even part of the narrative to a limited space – from Le Mepris to The Hateful Eight – the temptation is to consider the room as a stage, to use the space to its fullest extent. Ga-young has no such ambitions. Her characters languidly shuffle across the floor or slouch into deep sofas, and a few conversations are muffled exchanges between a boy and girl half-hidden by blankets or cushions.

It’s an apt metaphor for the film itself. Miss Ex is a movie into which one sinks, as one gradually gets to know the central couple, their history and their quirks, what they are and what they wish to mean to each other. It helps that Ga-young and Yong-joon have a natural chemistry, and excel at the half-frustrated, half-amused back and forth which makes their relationship so believable. It’s also rather reminiscent of Noah Baumbach; not only is it shot in black and white, but it also makes intelligent uses of those silences and half-pauses in conversation which are so much more freighted with meaning than mere words.

This is also, as so many first pictures are, something of a filmmaker’s film. Lingering shots of half-eaten plates of food or a pack of cigarettes alert you to the fact that this is a young director still finding her eye – not at all a bad thing, as the roughness and light experimentation really only add to the film’s charm.

And of course, as all films about youth are, Miss Ex is about the passing of time. Jeonghoon is constantly checking the clock and counting down until his sister or parents or girlfriend returns; cigarettes burn down; microwaves beep the end of waiting. But the apartment seems like a bubble within time, where our two tangled lovers can stretch out their tentative self-discovery to eternity. It works for you too: Ga-young has constructed a charming and thoughtful space where for 99 minutes you can sit back, relax and let time slip by.  4/5