Is your spouse financially cheating on you?

She might never have noticed the missing money had her husband not finally confessed that he had lost a hefty five-figure sum in a bad loan to a friend. But her spouse’s belated honesty didn’t win him any extra forgiveness. “I was just livid," the wife said. "That was our money, not his, and it stung that he acted behind my back. It’s about trust. I would never have done the same thing to him.”

Brad Klontz, a financial psychologist and managing partner at Occidental Asset Management in Burlingame, Calif., says he has seen such deception wreck relationships. Secret bank accounts, hidden big-ticket purchases, money lost on undisclosed bad bets or investments—all are forms of financial infidelity, when one partner believes there is open and honest communication about money and the other is lying about it.

And it’s on the rise. A January 2014 online survey conducted by Harris Poll for the National Endowment for Financial Education found that 33 percent of adults with combined finances admitted to having hidden a purchase, bank account, statement, bill, or cash from their significant other, up from 31 percent in 2011. Thirteen percent of respondents said they’d committed more severe deceptions, such as lying about the amount of debt that they owe or even how much they earn, and 10 percent reported that it ultimately resulted in divorce.

Sometimes you don’t know there’s a problem until you face a financial crisis, says Douglas Eaton, a financial adviser in Coral Springs, Fla. But red flags that should make you suspicious include:

Your spouse consistently changes the subject or becomes argumentative when you bring up money concerns.
He or she wants sole control of your finances or insists on keeping financial-account passwords secret.
You uncover hidden cash either in your home or in a bank account that you didn’t know about, or you discover new credit cards or lines of credit opened in your partner’s name.
You spot unexpected suspicious withdrawals from investment or other accounts.

If you’re dealing with a serious problem, such as a gambling addiction or stealing from household funds, it might be time for professional help. The American Association for Marriage and Family Therapy has a member locator on its home page. Or you might find a member of the newly formed Financial Therapy Association, a small but growing group of therapists who specialize in helping people with money problems.

If you think you can work things out on your own, the following tips might help.

Come clean.

Set up time to talk. “You can limit it to, say, 30 minutes to help reduce some of the stress it will cause,” said Bonnie Eaker Weil, Ph.D., a New York City family therapist and the author of “Financial Infidelity: Seven Steps to Conquering the #1 Relationship Wrecker” (Plume, 2009). A full disclosure of any financial infidelity that has taken place and an apology are in order. It’s also a good idea to talk about how money was handled in each of your homes growing up, as well as your money goals, dreams, and biggest fears. “Airing our associations with money helps each spouse understand why they react to it the way they do,” Klontz said.

Give and get equal access.

Set up joint accounts if you haven’t already to pay your bills and to save for mutual goals, such as vacations, car purchases, and retirement, Eaton says. Online access is best so that both spouses can monitor account information. “Also consider imposing spending limits you both agree to,” Eaton said. “For example, my wife and I have a pact that we won’t spend over $500 without a discussion.”

Then you can each open individual accounts with any remaining household funds that you can use to buy or save whatever you like—with no input from your spouse, which could reduce marital money stress. “I call this the guilt-free account, even if you’re just adding $50 or $100 a month,” Weil said.

Keep your word.

What happens if you can’t come to an agreement?

Identify a neutral third party—a financial planner, pastor, or therapist—who can help you work it out and begin to rebuild trust. “I’ve done this with my wife, and I find it has made me a much better listener,” Klontz said.

—Mandy Walker

This article also appeared in the September 2014 issue of Consumer Reports Money Adviser.