Men go wrong at 50. They have a design flaw that manifests itself in middle age. A bit like the glitch that blows a Freelander's head gasket at 60,000 miles, except that a 4x4 can be salvaged with money and a mechanic whereas a malfunctioning man must be scrapped.
You need to be quick to spot the warning signs: an intermittent grumbling in the background, a tendency to suddenly steer away from you and a lack of responsiveness to your charms all indicate that your man is heading for trouble. If left unchecked, that reliable, rugged, all-terrain husband who has driven you safely for 23 years is likely to veer straight off the road and dump you in a ditch.
Look at actor Tim Robbins. Aged 51, he has just swapped his long-term partner, Susan Sarandon, for a plectrum and a pop at a rock and roll career. That's The Shawshank Redemption ruined. If Robbins can't be bothered to hang around for the gorgeous Ms Sarandon, it seems unlikely that Andy Dufresne would sit patiently on a beach in Mexico waiting for Red to make parole.
These unhappy-ever-after endings to long relationships are commonplace: it happened to me earlier this year. I married Prince Charming. Then he hit 49, turned into the Big Bad Wolf and huffed and puffed 'til he blew my life down. I had two weeks out of the classroom, three months in therapy, and it has taken me until now to glue the pieces back together. So when he reappeared last weekend, clutching a heart-felt apology and two tickets to Paris, the reply "Not by the hairs on my chinny-chin-chin" may have been a more sensible response than grabbing my nightie.
So last Friday I abandoned my lesson planning and got on a train to Paris with the bastard who ditched me six months ago. Now when your husband has declared that he is no longer "in love" with you, a weekend in the most romantic city in the world is likely to come with technical hitches. Young lovers flee to Paris. Dysfunctional middle-aged couples should visit Middlesbrough, Newport, or anywhere with a transporter bridge and no indigenous nightlife. Wherever we looked there were youngsters locked in such passionate embraces that Robert Doisneau would have been hard-pushed to capture a couple who weren't licking each other's larynxes.
It wasn't an easy trip. We hit the tourist trail through an expensive shopping quarter around the Place Vendome. I posed outside Chanel. We marvelled at the jewellery in a tiny shop "where dreams are made", a slogan that also encapsulates my school's target-setting strategies. When we reached the Tuileries gardens, he held my hand, awkwardly. Then in the great vaulted cathedral of Notre Dame, we sat silently through Mass: two strangers in a foreign land. Finally, we threaded our way through dusky streets to a cafe in Montmartre where we drank wine and played cards.
We returned warily to our hotel room, uneasy at the prospect of the night ahead. What if we touch and there is no redemption? What if there is only desperate sex?
Next day, on the train, he brings me tea and a Danish pastry. What big brown eyes he has. I study his anxious, familiar face as he asks the inevitable question: "So where are we now?" I hesitate. "About five miles from Stevenage." He laughs. We are a long way from home but still travelling.
l Anne Thrope (Ms) is a secondary teacher in the North of England.