“Everything I know about marriage I learned in my cancer clinic.” I’ve been known to say this to my friends, maybe more than once, maybe even causing some of them to grind their teeth and grumble about Robin and Her Infernal Life Lessons.

I can’t help myself. I’ve worked as a breast cancer doctor for 20 years, I’ve watched thousands of couples cope with every conceivable (and sometimes unimaginable) kind of crisis, and I’ve seen all kinds of marriages, including those that rise like a beacon out of the scorched-earth terror that is a cancer clinic.

It’s a privilege to witness these couples, but the downside is I find myself muttering under my breath when my single female friends show me their ads for online dating. “Must like long walks on beach at sunset, cats,” they write, or “French food, kayaking, travel.” Or a perennial favorite: “Looking for fishing buddy; must be good with bait.” These ads make me want to climb onto my cancer doctor soapbox and proclaim, “Finding friends with fine fishing poles may be great in the short term. But what you really want to look for is somebody who will hold your purse in the cancer clinic.”

It’s one of the biggest take-home lessons from my years as an oncologist: When you’re a single woman picturing the guy of your dreams, what matters a heck of lot more than how he handles a kayak is how he handles things when you’re sick. And one shining example of this is how a guy deals with your purse.

I became acquainted with what I’ve come to call great “purse partners” at a cancer clinic in Waltham. Every day these husbands drove their wives in for their radiation treatments, and every day these couples sat side by side in the waiting room, without much fuss and without much chitchat. Each wife, when her name was called, would stand, take a breath, and hand her purse over to her husband. Then she’d disappear into the recesses of the radiation room, leaving behind a stony-faced man holding what was typically a white vinyl pocketbook. On his lap. The guy -- usually retired from the trades, a grandfather a dozen times over, a Sox fan since date of conception -- sat there silently with that purse. He didn’t read, he didn’t talk, he just sat there with the knowledge that 20 feet away technologists were preparing to program an unimaginably complicated X-ray machine and aim it at the mother of his kids.

I’d walk by and catch him staring into space, holding hard onto the pocketbook, his big gnarled knuckles clamped around the clasp, and think, “What a prince.”

I’ve worked at cancer clinics all around Boston since then, and I’ve seen purse partners from every walk of life, every age and stage. Of course, not every great guy accompanies his wife to her oncology appointment every day -- some husbands are home holding down the fort, or out earning a paycheck and paying the health insurance premiums -- but I continue to have a soft spot for the pocketbook guy. Men like him make me want to rewrite dating ads from scratch.

WANTED: A partner for richer or poorer and for better or worse and absolutely, positively in sickness and in health. A partner for fishing and French food and beach walks and kayak trips, but also for phone calls from physicians with biopsy results. A guy who knows that while much of marriage is a 50-50 give-and-take, sometimes it’s more like 80-20, and that’s OK, even when the 80-20 phase goes on and on. A man who truly doesn’t care what somebody’s breast looks like after cancer surgery, or at least will never reveal that he’s given it a moment’s thought. A guy who’s got some comfort level with secretions and knows the value of a cool, damp washcloth. A partner who knows to remove the computer mouse from a woman’s hand when she types phrases like “breast cancer death sentence” in a Google search. And, most of all, a partner who will sit in a cancer clinic waiting room and hold hard onto the purse on his lap.

Robin Schoenthaler is a radiation oncologist at the MGH Department of Radiation Oncology at Emerson Hospital in Concord. Send comments to coupling@globe.com. Story ideas Send yours to coupling@globe.com. Please note: We do not respond to ideas we will not pursue.

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