By Kevin Voigt When it comes to investing for retirement, one in five couples seem to be locked in a broken love triangle with their stock brokers, a recent NerdWallet/Harris survey found. Of couples who have retirement savings, more than 20% don't know how much they have invested; an additional 21% said they don't share details about how they're saving in their long-term investments with their partner, according to the survey. While we aim for discretion when it comes to cash, a successful investing relationship needs to be more of a ménage à trois with you, your partner and your stock broker.