You married her for better or for worse -- but you probably didn't imagine that "worse" could mean infidelity. Women cheat almost as much as men do, according to a study published in 2011 by Indiana University. Asking your wife outright if she is having an affair might be the best way to find out for sure -- but only, if she answers truthfully. In the meantime, changes in her behavior and appearance may indicate that she is being unfaithful.

Women usually cheat for emotional reasons, according to sex therapist Ian Kerner, author of "She Comes First" in the Fox News article, "Focus on Sex: Why Women Cheat." This is different from why many men cheat. A woman who is having an affair may pull back from her husband emotionally. She may no longer want to talk about her day, share her feelings or discuss her problems with you. If you try to ask her what is wrong, she may reply with a vague answer or simply say "nothing." At first, some husbands may enjoy their less-talkative wives, but it could be a sign of infidelity.

Let's face it: As time goes by, a woman might let herself go a bit between the demands of work and child-rearing. But a woman who is having an affair may suddenly start to pay attention to her appearance again. If your wife usually heads to the gym in her old sweats and a ponytail but suddenly starts wearing snazzy, matching athletic clothes and doing her hair before she works out, take notice: She could be trying to impress a guy at the gym.

Suddenly, your wife isn't there as much as she used to be. She goes out for "girl's night" more often, stays late and work and makes plans to be away from home on the weekends. She may make excuses for not spending as much time with you and may even say that she needs "space." She also makes excuses for not being intimate with you. All of these are red flags for infidelity.

She used to leave her laptop open -- but now it's always closed, and she has changed her email password, too. So has the password on her phone, and if a text comes in, she makes sure you don't see it. She takes calls in the other room and is vague when you ask her who called, or even who she was with last night. You catch her lying about which friend she was with or why she had to work late. Secrets and lies are a sign that your wife could be cheating on you, especially if she has never been secretive in the past.