Men and women differ, when it comes to fantasizing about sex with partners other than their husbands and wives. Overall, fewer women than men report such fantasies, and, more interestingly, women's fantasy seems to be more susceptible to contextual factors.
In 2001, researchers at the University of Vermont conducted research into the prevalence of what they called "extradyadic sexual fantasies," or, in other words, fantasies about somebody other than your primary partner. (OPTIONAL ASIDE- NOT FOR CREDIT- A common criticism of much sexuality research is that it is conducted on college students, and how much does their sexuality really reflect that of the rest of us? One thing I love about this study is that it actually included not just college students, but university employees as well, up to the age of 70. )
Hicks and Leitenberg's research suggests that about 80% of married women will sexually fantasize about men other than their husband, while 98% of men fantasize about women other than their wife. Environment and context has much more effect on female fantasies, than it does on men's. In women, things like how long they've been married and whether they are actually having extramarital affairs increased the chances that women will fantasize about someone other than their husband. These factors don't predict fantasy in men - in men, simply being male predicts that they will fantasize about people other than their wives or partners - length of relationship, happy or not, cheating or not, doesn't have any predictive value. In other words, it's hard to go higher than 98%.
Men and women also differ about who they fantasize about. Women tend to fantasize sexually about known individuals - past boyfriends, coworkers, friends, or their tennis coach. Women's sexual fantasies tend to include aspects of intimacy and relationship, so it makes sense that their fantasy lovers are those with whom there is some relationship, past, present or future. Men are more likely to sexually fantasize about people they don't know, or even just people that don't really have any identity per se, like faceless, bodiless vaginas and breasts (Where do you think the Venus de Milo statue came from, anyway?). Men's sexual fantasies tend to be far less relational in nature, focusing upon explicit, mechanical imagery, usually without any romantic or emotional context or factors.
This research is revealing of a few key points - first, the overwhelming majority of people do fantasize about somebody other than their primary partner. This research only examined the last two months. If it were a lifetime assessment, it's hard to believe that male rates might not reach 100%, and female rates would climb significantly. So, guess what? That guilty feeling you get when you think about sex with a man other than your husband? You can put that feeling away. Your fantasy is normal, and might not mean anything. A second thing is that even in fantasy, female sexuality is more contextual than male. It is driven more by relational cues and factors. So, when discussing female sexuality, at any level, we must address the relationship variables that are playing in the background.
Now, other research has shown that most people never, never tell anybody about their sexual fantasies, including their primary partner. People fear rejection and judgment. But maybe, just maybe, this research and article might prompt you to have a delightful conversation with your husband, and start discussing some of your sexual fantasies. He's male, so you are pretty safe (98% safe) to assume he's thought about other women. What would it be like, if you gave him permission to admit that, at the same time as you admitted your fantasies? Fantasies truly don't have any real definite connection to behavior - sharing these fantasies with your husband doesn't mean either of you are going to stray. But, isn't it more erotic to have a mental, AND a physical connection with your lover? Isn't erotic communication, and shared fantasy, a delightful thing? Try it.