Why do people in movies even go on vacation anyway? Aside from the occasional Stella getting her groove back, cinematic vacations never seem to go very well. At best, you’re plagued with one comic mishap after another like in “National Lampoon’s Vacation”; at worst, the mishaps are more sinister, “Turistas”-style.

Or you can find a getaway is a great time to deal with a crisis point in your relationship, which happens to all three couples in “That’s Not Us,” a straightforward and empathetic comedy-drama now out on DVD from Strand Releasing and available on Netflix. Director William Sullivan is clearly inspired by the French New Wave in his naturalistic tale of longterm twentysomething lovers who decamp for Fire Island for the weekend, but forget to leave their baggage on the dock.

Alex (Sarah Wharton) and Jackie (Nicole Pursell) are a lesbian couple facing intimacy issues, not having sex and unsure how to talk about it. James (Mark Berger) and Spencer (David Rysdahl) are a gay couple facing a crisis point when Spencer is surprised by the news that he’s been accepted to grad school — in Chicago. And Liz (Elizabeth Gray) and Dougie (Tommy Nelms) are a straight couple finding their competitive streaks are getting in the way of having a nurturing relationship.

It is key that none of these couples’ problems is in any way related to their sexual identity, and indeed, Sullivan and co-writer Derek Dodge could have just as easily shuffled the deck and given different problems to different couples. We see the tensions and disagreements start to build (a drunken game of Cards Against Humanity is always a great way to stir the pot), but because the dialogue is often improvised, the couples’ interactions feel authentic and not melodramatic.

Each couple finally hits a moment of reckoning, and then works through it towards a deeper understanding. “That’s Not Us” is a film about the work of longterm relationships, the constant need for open communication and trust, and the quiet, lasting rewards of such effort. The film’s structure feels a little tidy at times, as we can almost predict which couple’s turn is next for the dramatic reconciliation, a neatness that pushes against the messy authenticity Sullivan wants to evoke.

But the actors are all believable and likable, the score by Passion Pit’s Xavier Singh is moody and evocative, and the film’s we-can-work-it-out message is an appealing one. Best of all, they manage to figure things out to get to enjoy their vacation a little.