THERE'S A BLEAKLY COMIC bit in "We Don't Live Here Anymore," a searingly real drama about two couples cheating not just on each other but with each other, where a husband confronts the fact that his wife, Edith (Naomi Watts), has been sleeping with his best friend, Jack (Mark Ruffalo). "I think this might be a good time for me to go to the movies," Hank (Peter Krause) announces to the two folks who have been cuckolding him, just as they sit down at Jack's dining room table for a little heart-to-heart.

Funny, I was thinking the same thing.

Not that I wanted to leave. Far from it. Not when it was just starting to get good. (Hank, to make matters worse, is sleeping with Jack's wife, Terry, played by Laura Dern). It's just that this exquisitely awkward moment didn't feel like a movie to me. Rather, it felt like I was in the dining room with these people, experiencing every cringing, squirming beat like some kind of invisible voyeur.

Yup, it's that good.

Or that bad, depending on your appetite for this sort of feel-bad drama. Myself, I loved almost every minute of its psychologically and emotionally raw story of betrayal and healing, adapted by screenwriter Larry Gross from two short stories by Andre Dubus, whose work also inspired the great and equally gut-wrenching "In the Bedroom."

Mind you: I said almost every minute. I could have used a little less of what felt like director John Curran's overly ominous focus on train tracks and hurtling white water. At times, it seems certain that someone is about to get run over by a Metroliner or fall into the river and drown. As the husband of another critic put it after a recent screening, "There's enough real horror here without adding fake horror."

He's got that right. When Jack, a college literature professor teaching Tolstoy's "The Death of Ivan Ilyich" (symbolism alert!), informs his wife that he loves Edith, it feels less like a declaration of affection for another than a head-on blow meant to injure his spouse. And yet, there's something strangely appropriate about Curran's attention to the features of a threatening landscape, particularly to railroad crossing gates, the first of which descend, portentously, only a few minutes into the film, when it is clear that Jack and Edith are about to embark on their out-of-control affair (which, in turn, precipitates the one between Hank and Terry.)

Why do these people cheat? Lust, to be sure, but also a desire to punish their spouses for their own unhappiness.

"We Don't Live Here Anymore" is not, however, a morality tale. True to its metaphorical title, it's actually more than a geography lesson -- one whose subject is the shifting terrain of two broken, drifting marriages. Lines are crossed; people venture into the woods -- literally and figuratively -- only to get lost.

In this film, which is as harrowing a horror story as they come, one couple might make it out of that scary forest and one might not. Far be it from me to call "We Don't Live Here Anymore" optimistic, yet there's a ray of hope shining through all the gathering darkness that feels a little bit like the kind of lesson that can be learned only at the school of hard knocks.

In the process, the movie may leave its audience feeling a little battered (some might say betrayed) as well. Still, the film's honesty, along with its refusal to pander to Hollywood happy endings, is well worth the beating.

WE DON'T LIVE HERE ANYMORE (R, 104 minutes) -- Contains obscenity, talk of sex and scenes involving sex and nudity. At Loews Georgetown and Landmark's E Street Cinema and Bethesda Row.

Mark Ruffalo, from left, Peter Krause, Naomi Watts and Laura Dern play two unhappy, adulterous couples in John Curran's gut-wrenching drama "We Don't Live Here Anymore."