When we think of infidelity our minds go straight to the bedroom, but financial infidelity can be just as devastating. Sunday Morning talked with a relationship property lawyer about the problem.
A major study in the Journal of Consumer Research found similar amounts of financial infidelity among young and old and across genders and wealth levels. It also found the older people are the more vulnerable they are, as they have less working life left to save again.
Relationship property lawyer Jeremy Sutton from Auckland's Bastion Chambers says it's important to be honest and to be aware of what's going on in a relationship's finances, and there is lots that can be done to help protect both partners and the relationship from financial strife.
"[Financial dishonesty] can be a reason for splitting up, anything done in secrecy will cause problems in a relationship. Spending where it means there's financial stress, that's when people can look and say 'do I want to be in this relationship or not?'."
Financial experts, therapists and divorce lawyers point to a handful of typical reasons for financial betrayal, including addictions, affairs, abusive behaviour and differences in values.
Sutton says the most common cause for financial dishonesty in relationships is addictions.
"It might be that they're opening new bank accounts, it might be they're changing their behaviour, perhaps they say that they're going to a work conference in the weekend and it's not a work conference at all, it's something that involves spending.
"They might be changing their passwords... You generally have to look out: Is something different from what it was a few weeks ago?"
If one partner has a known addiction it is a good idea to protect any credit cards and joint accounts, including placing limits and passwords on accounts, overdrafts and the mortgage, he says.
"Make sure there are boundaries.
"It is going to be a difficult conversation. People don't like talking about money, people often don't talk about money at all. But really people should sit down every six months or every year and go through the finances. Because often there's one party that doesn't know what the finances are at all, they leave the control to the other party or the other party takes total control. They need to be interested."
When sexual infidelity occurs, affairs usually include financial infidelity and spending, such as hotel rooms or gifts, Sutton says. And while people try to hide the evidence, the plethora of information available now in the information age means something often gives them away.
"It may not be obvious how that money is spent... but there's been a portion of money that has not been spent on the relationship but has been spent on something else, and that's really aggrieving for that person."
Sutton says another troubling type of financial betrayal of a partner is where one person is controlling or abusive of the other partner's access to money.
"It's not justified, and we do see this a lot. Where there's a disparity of income between the couple, and the advantaged party perhaps is controlling the finances in the relationship.
"They come to see you and they talk about 'my income, my money', when it is always their income, and their money really. And it gets to the point where they're perhaps giving an allowance to the other person.
"That becomes what we call financial abuse under the domestic violence legislation, because they are controlling every move of the other person, as to how they're spending that money, when it's not justified. There are a range of agencies [to turn to], such as the community law centres, you can get legal aid - government funded aid, or you can contact a specialist domestic violence service such as Shine or Woman's Refuge."
Sutton says New Zealand law means after three years in a relationship, each partner is entitled to 50 percent of the value of their combined property if they split up - regardless of whether they are married or living together, and regardless of what each brings into the relationship. However, this is often not known by those in relationships.
He recommends couples talk about finances before any major spending decisions, and keeping track of their spending using data analysis provided by banking apps.
Those in a relationship should also be aware that assets and money can be wrapped up in legal trusts, which may not always be clear.
Most of all, he says communication and honesty is key.
"Sit down and talk about it, communication's much better now than when [problems] happen - people need to communicate, they need to open up about finances."