Financial infidelity. It’s not quite the same as other types of infidelity in your marriage, but experts say it can be just as damaging.

We talked to a panel of financial planners to sort out what it is and how to avoid it.

Several say they’ve seen it before, and it’s always unpleasant.

“As we were going through budgeting for some clients, there was just a shortfall every month in the budget that they just couldn’t figure out where it was,” Dave Henderson said.

He says one of their clients was funneling away funds for themselves.

You’d be in trouble for doing that at work, there’s a good chance it’ll get you in trouble at home, too.

What is financial infidelity?

Marty Walsh defines it as “a part of your personal financial life that’s hidden from your spouse, whether intentionally or not.”

Spouse in an important word there. All of the financial experts we spoke to believe financial infidelity is really only a problem when you’re in a marriage or domestic partnership where funds are tied together; when your partner’s actions could leave you on the hook.

Rebecca Kennedy expands that further.

She says financial infidelity is partly “when one [spouse] is doing something with their money, or money of the household, that the other doesn’t know about,” but also something, “that [the other spouse] wouldn’t agree to.”

When does it happen?

Kennedy says it usually happens when there’s a large gap in spending and saving habits between the two partners.

If the spender’s habits are out of control, they may try to hide that spending in order to avoid conflict.

The problem, however, is that money adds up.

The budget, if you’re on top of it, will usually point out those missing funds.

How do you fix it?

There’s a reason experts advise you be open and honest about finances with your partner, even if you have some separate accounts.

If your partner finds you have a secret account or some secret debt, “that could be really damaging to your relationship,” Walsh says.

A 2010 National Institutes of Health study found partners with shared finances were far happier and more intimate.

Walsh says being honest about your money leads to greater trust and brings spouses closer together, even in hardship.

He expects the opposite is true. Secret funds can drive a wedge into the heart of your marriage.

If you plan on staying married, there’s really only one way to fix it.

“It’s really important that the spender come clean if there’s something that they’re doing that the other person isn’t privy to, and that we start to address it as a team,” Kennedy said.