Many of us have a curious relationship with money. It's a more taboo subject than our sex lives.

Bring a sweetheart into the mix, and it becomes a strange menage a trois indeed. Turns out, we frequently hide our finances from the person we hold most dear.

Nearly half of the adults in a serious relationship have committed "financial infidelity," says Yahoo, which conducted an online survey of 1,750 people last month.

This means they lied to a mate about the cost of a purchase, or hid the purchase to avoid fighting about it. (Closets and car trunks are frequent hiding spots.) About 1 out of 10 has a savings account that a spouse doesn't know about, and slightly more secretly run up credit-card debt.

"It's almost like money is the third rail in the relationship. It's the charged one," says Dayana Yochim, author of The Motley Fool's Guide to Couples and Cash.

Women are more likely than men (55 percent to 41 percent) to financially cheat, Yahoo found. They also are more likely to break up with someone for lying about finances.

"Women are less confrontational than men," says Laura Rowley, a Yahoo columnist and author of Money and Happiness. Little white lies about money might seem worthwhile to women, she says, if they can avoid an argument.

(Just think of how many relationships have been saved by a less-than truthful response to, "Do I look fat in this?")

The Yahoo findings are further evidence that men and women approach money differently.

"For women, it's all about security," Yochim says. "You see that in the way they invest their money, as well. They tend to stick with safe investments where they won't lose money -- bonds and CDs.

"Men are about opportunity. They're sort of looking for the next hot stock. They tend to trade more frequently."

Not surprisingly, such differences in attitude can lead to conflicts. Money is often the root of breakups. It doesn't have to be. Discussing finances early can reduce friction later. Then you can let other factors, such as his friends or her family, pull you apart instead.

Honesty is the best policy when it comes to money. Timing is important, too. It's best not to be brutally frank during a heated quarrel. Honesty is best served cool.

You and your mate need to calmly discuss your financial goals and worries. If one partner feels financially insecure, for instance, you might agree to set aside six months in living expenses in a high-yield savings account instead of two months', Yochim says. "The goal here is a resolution, unless you like sleeping on the couch," she says.

It is equally important to men and women to have some financial freedom, where they can spend money without being judged, Yochim adds.

One way to achieve this is to agree upon a certain sum, say, $100 a week, that each can spend with no questions asked, experts say. It can't be too high. Yahoo found that people tended to agree that anything less than $500 was the most you could spend without talking to a partner first.

Sometimes money issues are a symptom of a deeper problem.

One partner might secretly spend because he or she is upset about getting stuck with the household chores, Rowley says.

Or, if you have a mate with extreme money issues -- he doesn't spend a penny or she can't save a dime -- you need to dig deeper into the cause of this. Attitudes about money are usually rooted in childhood, Rowley says.'

You don't, of course, have to divulge your financial laundry on the first date. But once things get serious, you must come clean.

Engaged couples should share their credit scores, experts agree.

"Thankfully, the credit score industry has put this all together and gave us a grade on how we handle our finances," Yochim says. This makes financial confessions easier, she says, like "'Guess what? I'm a B-minus student.' "

You can't talk about men, women and money without mentioning the annual relationship test: Valentine's Day.

The burden of this day undoubtedly falls more heavily on men. And it's not just Madison Avenue dialing up the pressure. Women are three times more likely than men to say getting a Valentine's gift is important, Yahoo found. And about three-quarters of women expect one.

Lucky for guys, lovers overwhelmingly say it's the thought that counts, not the amount spent. And 93 percent of women says there's no way better to express love than with a hand-written letter.

"You don't have to go overboard," says Yochim, adding that men can get a glue gun and make a homemade card.

"I'm now hated by women in the Baltimore area," she says. On second thought, she quickly adds, buy a card. "It's only $2.50."

Don't worry ladies, men plan to spend more than that. Men expect to shell out an average of $208 for Valentine's Day, compared with $165 for women.

Questions? Comments? Or to share tips with readers, contact Eileen Ambrose at 410-332-6984 or by e-mail at eileen.ambrose@baltsun.com