Cheating on your lover has become a multi-million dollar industry. With approximately half of people admitting to having been unfaithful at some point in their lives, Web sites like Ashleymadison.com are cashing in, beckoning online cheaters to meet with slogans like “When Monogamy Becomes Monotony.”

Yet while it’s easy to blame an industry that’s obviously sold its soul to the devil, what really instigates infidelity? Who is ultimately responsible for cheating? And are there ways to prevent your partner from going astray?

Personally, I can’t relate to cheating. I’ve never done it nor plan to. After all, dishonesty and lying are two of my biggest pet peeves. They’re inexcusable. To cheat on a lover is cowardly, selfish, and just plain wrong.

And cheating can take a toll on the mental, and maybe even the physical, well-being of both the cheater and the cheated –- both of whom are left with the emotional scars of lies and betrayal … or worse, the physical effects of an unwanted disease.

Still, I’ll admit that it’s easy to sit around and play Judge Judy if being unfaithful isn’t a part of your relationship resume.

So why do people cheat? Why do they risk so much for so little? After all, infidelity is not normal behavior, but the symptom of a much bigger problem.

On the most basic level, not everybody values monogamy, honesty, and intimacy. Yet, cheating is a lot more complicated than side-stepping a moral minefield. There are plenty of reasons — or rather “excuses” — the love forlorn give for getting in bed with another, including:

They don’t feel loved. Cry me a river. Don’t we all feel that way at some point?

They have fallen out of love. Then get out of the relationship!

Their needs are not being met. Are they being expressed? Much like the Psychic Network, mates don’t make for mind-readers.

They just need a friend. You’ll have better luck finding that friend at the Society for the Prevention of Cruelty to Animals than a brothel.

They’re struggling with partner incompatibility. You should’ve thought to play 20 questions before you became too intimately involved.

They are dealing with larger commitment issues. Only you are to blame for the ball and chain at your feet.

To add insult to injury, many try to justify their dishonesty as having been for “their partner’s protection.” They weren’t being hostile in playing "Naked Twister" with the next door neighbor — honest. They were doing it out of “love.”

Reality check: Cheating is not an expression of love, nor a way to save your relationship. People cheat when they want to avoid tough decisions, when they aren’t up for the hard work required of a long-term romantic relationship, or are unable to break things off mercifully. They’re completely disregarding the fact that when you cheat, you’re breaching an agreement, specifically that one involving “’til death do you part.”

That said, the cheater may not be the only one at fault.

I know, I know, you should never punish the victim. But a relationship is a two-way street.

If you’ve been cheated on, there were likely some relationship red flags you ignored that could have prevented this ordeal. The lack of sex issue is a perfect example.

Many cheaters let their partners know that they long for more than the missionary position, that they want to have oral sex, that they want to try mummification the next time you play naughty nurse ... They’ve begged and pleaded for more sexual and emotional intimacy. You may vaguely recall that your response likely involved any of the following:

Defensiveness: “Am I no more than an object to you?” When you’re stone cold, well then yes.

A lack of sympathy: “That’s your problem, babe, not mine.” Guess what? When you commit, your problems are our problems.

Justification: “We have kids. We’re supposed to be sexless.” Parenthood does not have to be passionless.

Being dismissive: “You know I retired from adventure sex years ago. Isn’t that why we just bought you that brand new PC with gaming hardware?” If this were customer relations, then you just dropped the ball on maintaining product loyalty. Even the most faithful of consumers will switch brands when a company fails to recognize their needs.

Major character flaws aside, is it any wonder that a cheater is angry, frustrated, desperate, and vulnerable to any home-wrecker hyena ready to scandalously scavenge your union with sexual antics? You’re committing emotional abuse in depriving your partner of sexual intimacy. If you’re not willing to put some effort into your relationship, there are thousands of people, found with a few clicks of the mouse, who will.

While I just used a sexless union as an example of why a partner may commit adultery, realize that sex is usually not the purpose of an affair.

As stated in Frank Pittman’s "Private Lies: Infidelity and the Betrayal of Intimacy," many cheaters admit that sex is better at home. Affairs are emotionally complex, with a cheater seeking far more than sexual gratification in cozying up with another. Furthermore, it’s not the sex, per se, that will destroy a union, but the lies, secrecy, confusion and disorientation couples must grapple with.

So what to do? Unless you’re involved with a famous cheater like Jude Law, David Beckham, Usher, or Hugh Grant, you don’t have the luxury of the paparazzi busting your lover for you.

You could spy. Invest in some really good, discreet monitoring software, like Spectorsoft Spyware, which secretly records incoming and outgoing email, instant messaging and chats, keystrokes typed (including passwords!), and Web sites visited.

Or, preferably, nurture and prioritize your relationship. Think of your partner as a pet dog. If you don’t take it out to do its duty, it’s going to make a big, stinky mess.

If you’re worried about turning into a cheater (or committing a repeat offense), yet you can’t love the one you’re with, invest in a blow-up doll. Just keep your plastic passion at home, as the only thing worse than getting busted for cheating is getting arrested for indecent exposure with an inflatable, anatomically correct doll. (Yes, this has happened.)

Or grab your favorite form of erotica and spend some quality time with none other than yourself. Sound less than appealing? Just remember that in some societies infidelity is justification for murder.

In the Know Sex News

Who’s smarter now? A U.S. Census Bureau survey confirms that women are outperforming men when it comes to schooling. (I bet Sigmund Freud, who deemed women less intelligent than men, is turning over in his grave.) During the 2006-07 school year, about 33 percent of women 25-29-years-old earned a bachelor’s degree or better, while only 26 percent of males achieved such. So how does this apply to the dating scene? Boasting brains is no longer going to cut it for guys. The lack of letters and periods after his name is going to further hamper his ability to impress as far as job and income go.

Chlamydia can foil his fertility too. While we typically hear that chlamydia can result in female infertility, a recent study found that this sexually transmitted infection can have the same impact on men. Researchers examined the sperm of 143 males infected with both chlamydia and mycoplasma infections, finding that the level of DNA fragmentation in their sperm was 3.2 times higher than that of non-infected men. The sperm also had defects in shape and reduced motility and concentration. The good news? After both partners are treated for this bacterial infection, most couples become pregnant.

Forget Barbie when you can be pretty like a porn star. Nair, the makers of hair-removal products, seems to think that no girl is too young for her first Brazilian. With its release of Pretty Range, a line of wax and chemical products aimed at 10-to-15-year-olds, the company is basically encouraging youth to rip the hair from their barely pubescent bodies. As if these “first-time hair removers,” as Nair prefers to call them, have that much to remove.

Dr. Yvonne Kristín Fulbright is a sex educator, relationship expert, columnist and founder of Sexuality Source Inc. She is the author of several books including, "Touch Me There! A Hands-On Guide to Your Orgasmic Hot Spots."