If you're secretive about your finances and constantly hide purchases from and lie about your debt to your significant other, you're having a financial affair, experts warn.

This can lead to a serious breach of trust in your relationship, so much so that your spouse can see it as cheating, which can in the worst case lead to divorce.

So, what constitutes a financial affair?

A financial affair is when you spend a significant amount of money on anything without your spouse knowing about it, explains Nozuko Makhunga, a certified financial planner at Absa Wealth and Investment Management Distribution.

She also lists hidden debt and undisclosed loans to family and friends as you're having a financial affair.

Charles Pitt, private client wealth manager at Alexander Forbes Wealth, warns couples against spending more money on yourself without regard for your partner's feelings.

"If you spend more on yourself without being considerate of your spouse's needs, it can easily breed lack of trust, can be seen as cheating and ultimately lead to divorce for married couples," he warns.

Financial affairs can be traced back to when you were single where you either ignored the principles of budgeting or had impeccable money management skills, and then marry a partner who is quite the opposite. Instead of talking about money right from the start, you avoid the topic altogether which often leads to resentment and a complete breakdown of trust.

Makhunga says hidden debt for example is already a breach of loyalty and trust. The longer you keep your debt a secret, the harder it is to open up to your partner at a later stage. "Always keep in mind that a problem shared is a problem halved."

Another contributor to the loyalty struggle is undisclosed loans to friends and family that are often never paid back.

This can make your partner question your ability to make sound decisions, and adding insult to injury is the person borrowing the money trying to justify why it's okay for them not to repay the loan.

Giving your partner a seat at the table before granting the loan will get you both on the same page in terms of repayment or whether to write it off as a gift, Makhunga says.

Also, spending money over the festive season with friends seems like the natural thing to do to unwind, but it can quickly ruin your finances and your relationship if you're overspending - and without your spouse knowing.

Both Makhunga and Pitt warn that "financial affairs" are amplified over the holiday season when you are more relaxed and eager to spend more than usual to reward yourself for working hard throughout the year. This, however, can lead to resentment in the relationship, especially if one partner is responsible for budgeting and paying the bills.

Makhunga says it's important for you to review your family budget often to insure you and your partner stay on the same page. Pitt and Makhunga share more tips on how to avoid a financial affair:

• Have an open and honest discussion to clear up any assumptions about each other's attitudes around money. This will help align your thinking and can help you achieve your money goals smoothly and faster. Stressful situations are not the ideal time for you to discover your partner's differences in spending habits, they caution;

• Understand the household cash flow, especially if you're not the one actively taking care of the bills or household spend. This will ensure you both know how much money is available for some festive fun;

• Be open and transparent if you plan to spend a lot on a hobby, friends, family or even yourself. The more time you give your partner to prepare for your leisure, the less disagreements you are likely to have;

• Get help if the spending gap between you and your spouse seems impossible to bridge. A financial adviser is an excellent resource to consider as they help you understand your attitudes towards money, how those attitudes developed and how they can differ between couples; and

• Reconcile different money beliefs and upbringings. The old idea that opposites attract is romantic, but we are often drawn to partners whose personality and style complement our own. Differing beliefs about money is something that needs work from both of you to unlearn old habits and learn new disciplines that will grow your partnership.

• Constant communication about money will help you both determine your own boundaries around spending, debt and your tolerance levels - all with the goal of aligning your financial goals, Makhunga advises.