“Why can’t you just be happy for me, and then go home and talk behind my back later, like a normal person?”

So laments Lillian to Annie as their once-close friendship derails in the 2011 hit movie, Bridesmaids.

Lillian (played by Maya Rudolph) and Annie (Kristin Wiig) have been best friends since before they had breasts. Nothing can come between them—they share keys to each other’s apartments, secret glances, and a talent for skewering men’s sexual habits. Annie’s been sleeping with a cad since her business and relationship went bust. Lillian’s convinced her boyfriend is about to break up with her. But the men are a sideshow to the true bond. Over coffee and chocolate cake, Lillian and Annie laughingly propose to one another, “Will you marry me?” “Yes!” they both exclaim.

Instead Lillian gets engaged to Doug, and Annie responds with, “Oh, my God! What is happening?” Lillian and her fiancé coo to one another over the phone; when Lillian tells him how happy Annie is for them, Annie calls from the background, “No I’m not!” Her forced, manic laughter quickly subsides into a crestfallen expression as the contrast in their life trajectories becomes all too clear. Still, there’s no question that Lillian wants her best friend to be her maid of honor, and that Annie is honored indeed. She’ll put on a happy face despite her misery, and even sincerely mean it.

Until she meets Helen, Lillian’s new friend, who is richer, prettier, thinner, better connected—and who never misses an opportunity to flaunt it over Annie. Worse, it appears Helen has supplanted Annie as Lillian’s best friend.

Hilarity ensues as envy, competition, anger, galloping diarrhea, and all hell break loose.

Shit happens when there’s disparity between best friends, or between what they profess and what they feel. Especially when someone else comes between them. I can relate. What woman can’t?

In my case, my best friend, Sharon, responded to my engagement with, “How bourgeois!” She was my maid of honor, and although she didn’t ground any planes en route to the Bachelorette party, she was late to the wedding and called me a Nazi for being uptight.

Of course it’s more complicated than that. Sharon was never as rotten as our bridal saga makes her sound. Years before, when we took a four-month, post-college trip, she even nursed me tenderly through my own episode of galloping diarrhea in a Tel Aviv youth hostel after an unfortunate encounter with unwashed strawberries. Besides, I was often a Nazi.

We had a long history of ups and downs, chortling over in-jokes but also treading carefully amid landmines. Sometimes a misstep would lead to a blow-up, until we couldn’t bear the distance anymore–our conciliatory letters often crossed in the mail. Eventually our signals got hopelessly crossed. I don’t remember the details, but I do remember feeling like I’d been punched in the gut. Our final rupture knocked the wind out of me for years.

My break-up with Sharon is not unusual. The details vary, but practically every woman I know has a rupture story, complete with endless obsession and wounds that take forever to heal. Sometimes the rift is mutual and obvious. Often it’s silent, with one or both friends claiming that everything’s fine while secretly feeling adrift, even hostile. As Lillian’s opening remark reminds us, it’s normal for friends to be two-faced.

But why? Why are ruptures in women’s friendships so common? And so painful?

What do you think? Can best friends ever live happily ever after?