Winner of the Waldo Salt Screenwriting Award at the 2004 Sundance Film Festival (for Larry Gross's uncompromising script), "We Don't Live Here Anymore" would make a fitting companion piece with Neil LaBute's stinging 1998 drama, "Your Friends & Neighbors." Both films harshly, but accurately, portray the destruction of two marriages between adulterous friends, their unfaithful actions stemming not only from desire and unhappiness but also as a subconscious way of vindictively getting back at their partners for the mistakes they have made. "We Don't Live Here Anymore" is knowing and comprehensive in the large and small details that make up adult relationships, and, like "Your Friends & Neighbors," is fearless in the way it pushes forward into darkness even at the risk of revealing the sometimes very ugly sides of its characters. This two-picture marathon might not make for upbeat viewing, but they offer challenging rewards for audiences that stick with them and are never less than fascinating.

Jack (Mark Ruffalo) and Terry Linden (Laura Dern), and Hank (Peter Krause) and Edith Evans (Naomi Watts), are as different as night and day when it comes to how they raise their families and handle their households—the Linden's are loose, scattered, and messy, while the Evans' are quiet, clean, and orderly—but they do share one similarity: their supposedly happy marriages are deteriorating under their noses, and no one seems to be capable of doing anything about it. Trouble, it seems, has been brewing for these couples for quite some time, but, as the film opens, Jack and Edith make a mutual choice to sleep together that gradually sends all four lives into a veritable free-fall.

Before long, they are sneaking around behind the backs of Terry and Hank, making excuses to leave so that they can spend time together in the woods and at motels. One part of them fantasizes about the danger in getting caught, while the other half is horrified by the consequences—Edith knows Hank has cheated on her in the past, but cares for friend Terry enough to regret her betrayal. Meanwhile, Jack is hungry for something new and different, and doesn't like that homemaker Terry drinks too much and does little around the house while he works all day, but isn't prepared to give up his two children and the comfortable life he has built for himself. When Terry and Hank inevitably discover the untruth that has been going on between their respective spouses, Jack's reckless suggestion—that perhaps Terry and Hank should sleep together in return—puts the strength of their love for one another to the ultimate test.

Based on "Adultery" and the title tale, two short stories by Andre Dubus (whose "Killings" was adapted into 2001's "In the Bedroom"), "We Don't Live Here Anymore" is a piercing psychological drama full of deep-seated wounds and simmering resentment. Director John Curran is adept at handling the unhealthy human relationships between these four flawed people; he takes a long look at them without making judgments—it is up to the viewer to make their own assessments—and refuses to sugarcoat what in lesser hands might have become a shaggy melodrama. People make mistakes, Curran and screenwriter Larry Gross (1999's "True Crime"), appear to be saying, but can what Jack, Terry, Edith, and Hank do through the course of the film be chalked up to mere weakness? And no matter how much love may be present between two people, at what point does a marriage—or any relationship for that matter—move past the point of no return and become unsalvageable once the damage has been done?

The performances by Mark Ruffalo (2003's "In the Cut"), Laura Dern (2001's "Novocaine"), Naomi Watts (2003's "21 Grams"), and Peter Krause (HBO's "Six Feet Under") are inexorably exceptional across the board, each one developing a particular and differential character that elicits both sympathy and empathy in the viewer without having to ask for it. Ruffalo's Jack makes bad choices without considering what it may mean for his future and that of his family's and friends', steaming carelessly forward until things start crashing down around him. Dern's Terry takes out her anger toward husband Jack through fights and yelling matches because she knows no other way to handle her insecurities, but there is a quieter sadness Dern brings to the part that makes her seem palpably real. Watts' Edith, like Jack, begins her affair with him heedlessly, but she doesn't put more significance on their secret trysts than they deserve; even after sex with Jack, she sometimes can't help reasoning to him that she is doing what she is doing because Hank never reciprocated her attempts to mend their problems. And Krause's Hank, a creative writing professor at a nearby university who is having trouble selling his work, takes his own actions and those of his wife with a grain of salt. While hanging out with friend Jack, Hank isn't above admitting that sex outside a marriage for mere carnal gratification is something he does on occasion, and never regrets as long as there aren't any real emotions involved.

With the exception of a couple confrontations and minor character actions that strike one as a little forced (most of them are, indeed, seamlessly plausible), "We Don't Live Here Anymore" is a highly charged, poignant study of the imperfections within human nature and the frailty of otherwise powerful love relationships. The diverse children of both couples—Jack and Terry have a playful young son (Sam Charles) and daughter (Haili Page), while Edith and Hank have a somewhat lonely daughter (Jennifer Bishop) around the same age—are also written with a touching depth that suggests they are more perceptive than adults give them credit for and run the risk of becoming emotionally damaged in the future if their parents don't become more attentive to their feelings.

Sumptuously photographed in what appears to be a luscious, color-strewn, autumnal New England suburb (but filmed in British Columbia) by Maryse Alberti (2001's "Get Over It"), "We Don't Live Here Anymore" receives much of its power by understanding that there are no easy answers when it comes to what the four central characters are going through. As the ending arrives, director John Curran leaves the viewer questioning whether things will get better or worse for all involved. One thing is for certain, however—they all will escape from the rubble of their broken lives with a newfound strength they likely never conceived they were capable of having.