Most women have been taught since childhood to be "good little girls", "behave like a lady", and "grin and bear it”. Remember hearing the saying "little girls are made of sugar and spice, and all things nice"?
Fast forward to the 21st century, where women are now allowed to be tough, to say NO, to speak their mind, to become CEO's and to enjoy sex. Women have become more assertive and in tune to their needs, wants and desires.
Some men like the fact that women are able to "talk the talk" and "walk the walk" while others feel intimidated by it. Without a doubt, this change has had a great impact on relationships between men and women, specifically the actions and behaviors of women.
According to 2012 statistics from the Journal of Marital and Family Therapy, 14% of married women have cheated compared to 22% of married men. Although women are not exceeding men in cheating, women are having emotional affairs and sex behind their man's back. However, when a woman cheats, she is usually cheating for emotional intimacy while a man usually cheats for physical pleasure.
Women are still emotionally invested in their relationships. Women want to feel desired, wanted and irresistable. It's quite phenomenal how far women have come in this world, from women's lib, entering the workforce, becoming professionals, breadwinners of the family, and now getting their needs met; even if it means cheating. Now get ready to see what I reveal about why women cheat.
1. Lack of attention and intimacy: 
How long can you go without receiving love and attention before you look somewhere else? Some can go for only days or weeks, and others can go for years. However, in general, women need and desire intimacy, physical touch, and mental and emotional attention. If you are not receiving this from your husband or boyfriend, it will only be a matter of time and you may seek it from another i.e. a caring guy friend, the attentive guy who feeds your emotional needs at your workplace, or the hot trainer at the gym. Women deprived of attention, compliments, and compassion; usually have emotional affairs. That doesn't mean it won't lead to sex, but initially they crave the attention and compassion that has been absent from their relationship.
2. Revenge:
Being cheated on is a very difficult act to forgive. For those of you who have been cheated on, you know how awful it feels. You feel deceived, hurt, angry, sad, numb and even violated. It also affects your self-esteem. At the moment you find out your man cheated, your whole body begins to shake, you begin to sweat, your stomach drops, and you feel nauseated. Clearly, it negatively affects your relationship, your mood, behavior, and your ability to trust the cheater ever again. When you have been cheated on, some of you may want to get revenge by making them feel the way you felt. This can lead you, to do the cheating next. The biggest truth is that cheating never solves a relationship problem. Communication, assertiveness and increasing passion and romance in your relationship are a much better solution.
3. Bad sex:
Women need to feel desired and experience REAL orgasms during sex. If women are getting bad sex, not enough sex, non-emotional sex, or "wham-bam-thank-you-mam" sex, you may eventually lose interest in the relationship and look elsewhere for GOOD sex! This creates a temptation to seek sexual or emotional satisfaction elsewhere. In my opinion, it's best to communicate your needs to your man with the hopes that he will step it up a notch. You can do this on your own or with the help of a sex therapist.

4. Weight loss/plastic surgery:
Male attention increases quickly after a boob job, a butt implant or weight loss, and so does your self-confidence. With all this male attention, your temptation to cheat rises, and it takes more self-control to resist some of those male offers. Once you realize other guys want you, your desire to act on it may have you feeling euphoric. However, be careful, act wisely and make your pros and cons list.
5. Financial independence:
When you feel financially dependent on your husband or boyfriend, it's more difficult to speak up in arguments or leave the relationship. The fear of being alone and financially unstable keeps you in a one-down position. Now that women make their own money, enjoy working, and are good at it, the need to stay in an unhappy relationship is not necessary. That feeling of power and independence can be like seeing the red carpet laid out for you; all the way to those other fish in the sea.
6. Low self-esteem:
When you feel insecure about yourself, you have a need to seek validation from others. This can be in the form of sexual, emotional, or intellectual attention. When you don't love or value yourself, you may project that onto the person you are in a relationship with, and believe they don't love or value you. Even if your husband or boyfriend loves you greatly, you still may cheat because you find it hard to accept their unconditional love. I suggest reading one of the many self-help books out there on building your self-esteem, or get some counseling to help improve self-confidence.
7. Feeling under-appreciated:
When you are in a relationship, you like to please your man. Cooking a romantic dinner, buying sexy lingerie, and listening with your heart, are just a few ways you may show your love and appreciation. So what happens when you don't hear "thank you, please or I love you.” Holidays and birthdays come and you don't receive anything meaningful, nothing at all, not even a verbal acknowledgment. We all have thresholds, and once yours is reached, you may decide to act on a "thank you, please, or I love you" coming from another direction. Let your man know he may lose you if he continues to take you for granted.
8. Bored:
He doesn't spray on that good smelling cologne anymore, his clothing is wrinkled, stained or way out-of- date. When he comes home from work (assuming he has a job), it's the same old thing; "what's for dinner"? When the weekend comes, he says he's tired and just wants to relax at home, or go out to the same sports bar you go every weekend. The routine is the same over and over again. You are no longer on the same page. You barely have anything in common. You are feeling emotionally distant from him. You find yourself looking at other prospects and fantasize about being with someone else. You begin to feel excited (something you haven't felt in "forever") just thinking about it. There are many ways to spice up an old, tired relationship. Boredom is something that can be resolved with a little, or sometimes a moderate amount of effort. It requires both of you introducing new ideas and behaviors, and some spontaneity. Be sure of what you want.

Source: DivorcedMoms