“The number one reason for divorce is not infidelity or falling out of love,” the 61-year-old Canadian mutual funds magnate tells Entrepreneur on the set of the hit reality show. “It’s money. It’s one partner outspending the other. It’s going into debt. It’s not respecting the joint finances. If you avoid doing all of that, you’re in it for the long haul. If not, forget it.”

The shrewd Canadian billionaire tied the knot with his wife, Linda, in 1990, all of a quarter of a century ago. He credits their lasting union with one thing — and it’s not necessarily love, passion or sex. The real reason they’re still going strong: They’re on the same page about money, and they’d better be. O’Leary’s other half is an actively involved executive at their successful wine company.

Together the pair have two grown children, Savannah, a college student, and Trevor, a music producer, neither of whom will inherit their parents’ fortune by design. They weren’t always a perfect or even whole family unit. O’Leary admits that he was largely “an absentee parent” while building his empire, which nearly ended his marriage.

While O’Leary recommitted himself to his wife, his friends left theirs. The author of Cold Hard Truth: On Family, Kids and Money (Doubleday Canada, 2011) says “all” of his friends are divorced and he’s learned a lot from watching their marriages crumble.

The worst mistake he says most of his divorced friends made was failing to thoroughly financially vet their partners, just as they would a potential business partner, well before popping the big question. Doing so, whether on your own or with the help of a professional, is something he highly recommends to anyone considering coupling with someone, in sickness and ideally in fiscal health, til death do them part.

Don’t stop at running a financial background check on your future husband or wife. Demand a prenuptial agreement, O’Leary further advises. “It forces you [and your betrothed] to tell the truth about your financial past…It’ll save you hundreds of thousands of depression and grief and it may save your marriage to find out.” A prenup can also make it easier to divide your assets clean in half should you exhaust your options and eventually split, which he thinks you should never do if you have children together.

“If you have kids, you should absolutely not get a divorce because it’s never better the next time,” he says. “It’s the same thing over and over again, except now you don’t have a family any more. It’s awful for everyone, especially the children.”

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Instead, if your goal is to stay together for good, tighten up your collective purse strings, respect the family budget and hang in there through the tough times. “When your marriage hits the rocks — and they all do — treat it like the business partnership that it is and you’ll pull through. I’ve seen it happen.”

This piece was originally published on Entrepreneur.