Most couples have a shared -- or at least a mutually understood -- view of what represents marital infidelity. Some might see texting with an ex without telling their current partner as cheating; others might not insist on that level of transparency, but would draw the line at physical contact.

Of course, in some couples, partners may not wholly agree on the details, and others may have hazier guidelines about where romantic cheating begins. Financial infidelity faces a similar problem of definition. One partner may view going off budget to eat lunch out as no big deal, while the other might see that as being financially unfaithful.

That at least partially explains why 34% of married Americans report that they aren't always "financially faithful" to their spouse, and 39% say they don't believe their spouse is entirely financially faithful with them, according to a new survey from TD Ameritrade.

Money issues can also lead to conflict even when one member of the couple is not "cheating." Over the past year, the survey's 1,000 married respondents had an average of 4.3 arguments about money with their spouses.

A man and a woman each hold half a torn paper heart.

Don't let not talking about money break up your relationship. Image source: Getty Images.

Marriage changes things

The good news is that marriage can also lead to more positive financial habits. According to 37% of those surveyed, for example, getting married did cause them to "pay more attention to their finances." In addition, 33% of men and 28% of women said they had been saving more money since getting married.

The among the survey's other interesting results:

  • 32% of married men and 28% of married women started to worry more about the future after they got married;
  • 30% of married Americans said, "the moral support that keeps each other on track is the biggest financial benefit of getting married";
  • 30% of married individuals rely on their spouses to help manage their savings and investments.

"For many Americans, wedding bells serve as a wake-up call to get their finances in order as they now have a partner to think about," said TD Ameritrade Managing Director JJ Kinahan in a press release. "Having a spouse, and perhaps for some a family, can encourage better financial habits, deter overspending, and keep long-term goals in focus."

What can you do?

One thing that the results above make clear is that not enough married couples talk about money. It's easy to mistrust your significant other if you aren't mutually putting all your cards on the table. And it's perhaps understandable why we might be tempted to postpone those difficult discussions indefinitely -- who really wants to begin a conversation that's likely to end in one or both of you agreeing to change your habits?

Get over it. These conversations should happen early, and they should happen often. Ideally, if you have room in your budget, each member of the couple should get a weekly or monthly allotment of guilt-free "fun" money -- cash you can spend on whatever you want without having to explain anything to your partner.

That amount might be small for some couples, but the flexibility it builds in might help prevent deeper financial infidelity. If you and your spouse know you can buy your comic books, concert tickets, pizza, handbags, or whatever else and still be working within the budget you've both laid out, there's simply less reason to lie.

Daniel B. Kline has no position in any of the stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. The Motley Fool has a disclosure policy.