My husband and I are in our 50s, married 25 years. I married for life, but I didn’t expect our initially happy marriage to turn into a dull housemates situation. With our children away at college, there’s no distraction from my husband’s lack of interest in having a fun, interesting life or even trying to be interesting to me. Most disturbingly, he isn’t interested in sex — at least with me — though I’m fit and still get called “beautiful.” I can pleasure myself, but I’m despondent at the prospect of spending the last decades of my life no longer being desired or even seen as a sexual person. I’m envious of my 50-something friend, now shacked up with her new partner. They are so effusively fulfilled together — domestically and sexually, I’m told — it makes me want to vomit whenever we meet for dinner. I can only imagine the fun and sex they’re having. Do you think I should follow their lead?

—Sex-Starved Bored Wife

There’s “Marriage, The Fantasy” — the gauzy gloriousness you see in wedding dress commercials — and then there’s “Marriage, The Unadvertised Reality”: Eventually, your spouse could die at the breakfast table, and you might not notice till dinner.

Couples whose spousalship erodes to this point tend to feel guilty (yet mystified at where they went wrong). They’re unaware they’ve been set up to fail thanks to impossible-to-meet modern expectations for marriage. “For thousands of years the theme song for most weddings could have been ‘What’s Love Got to Do with It?’” observes historian Stephanie Coontz.

Until about 200 years ago, marriage was a vital system for powerful moneybags families to forge political alliances, merge fortunes, and even make peace treaties (lest Europe play host to the, um, Hapsburgs and the McCoys). We of the stinking masses did this on a smaller scale, like by marrying off our daughter to the son of the farmer with the enviable potato fields butting up to ours.

In other words, the common modern expectation that a spouse be one’s lifetime romantic and sexual excitement provider gives marriage a job it was never set up to do — and really can’t do — just when medical advances have us taking longer than ever to go facedown in the Cream of Wheat.

Marriage modern-style has its pluses: among them, an on-site best friend, a stable environment for raising kids, two-fer tax benefits, and higher living standards. And let’s be frank: It’s ideal to live with someone who’ll do more than lick his paw while you thrash around on the living room floor from a seizure.

Unfortunately, there’s no stopping the “hedonic adaptation,” the inevitable dulling of marital excitement. “Hedonic,” from the ancient Greek word for pleasure, with “adaptation” describes how we quickly habituate to changes in our lives, positive or negative. That boob job or the bummer diagnosis stops giving us the lift or gut punch it first did, and we swing back to our baseline level of happiness or gloom. In a marriage, assuming things don’t go ugly, the early lusty romance gives way to “companionate love,” the comfy dog-chewed old slippers of long-term partnership.

There is a defibrillator of sorts for flatlining marital excitement: an ongoing variety of surprising experiences — big and small, daily and weekly. Neuroscientist Wolfram Schultz finds that “unpredictable rewards” — aka surprises — can be three or four times as exciting to us as those we’re used to. To take advantage of this, spouses might alternate weeks bringing each other on a mystery date — taking into account personal preferences and medical issues, lest the surprise take a surprise turn: “Betcha didn’t guess we’d be drinking Benadryl nightcaps in the ER!”

Admittedly, this is rather weak tea to throw at the problem disturbing you most: being sexually abandoned by your husband. It’s probably impossible to solve and likely would be even if he wanted to want you again. We’re sexually excited by the new and out of reach, and you can’t become a sexy stranger for him to pursue — or even fake it plausibly.

You went into marriage with the best of intentions — marrying “for life” — but you’re now left with two options: 1. Part company with having any sort of sensual relationship that doesn’t require vow breakage. 2. Part company with your husband. If you’re inclined toward the latter, some inner voice might rise up to scold you, “Whatever happened to ‘Till death do us part’?!” Sure, that’s the deal you signed up for, but consider whether you think living the next 30 years like you’re sexually embalmed should count. Personally, as a never-married, seize-the-day type, I’m planning to be the hussy of the senior care facility — the subject of endless gossip by resentful elderly busybodies.