why do women seem to want WHO they can't have?

Honestly I think when you are with some one you are happy and confident and people pick up on that.

that would make complete sense actually.

A little reading. Apparently my perspective isn't all that crazy after all.
What You Need To Know

"Girls want what other girls have."

Here’s the scenario: You've been single for a while and no matter how you try to woo the ladies, your suave pickup lines and quips bear no fruit. Then, one evening when your dignity has all but bottomed out, you make nice with a jaw-dropper and soon find yourself in a new relationship. Things progress beautifully, and as they do, you notice that you’re getting an abnormally high number of bicep-squeezes, do-me eyes and knee-slapping laughs from attractive women who aren’t yours to bring home. In an unlikely turn of events, it seems that your success with one woman has made you successful with all women. So what gives?

Like a moth to a flame, single women are drawn to a man in a relationship. It’s a fascinating coincidence -- one that is frustrating and unfair for the newly tied-down gentleman. Just when the gettin’s good, he’s not allowed to get. Nevertheless, the reasoning behind this phenomenon will help you be a better man, whether you’re single or taken.

Women want what’s off limits
In the Garden of Eden, Eve sinks her teeth into the one piece of fruit that God instructed her to avoid -- so began a long line of women who wanted, oh so badly, what they could not have. We see the same trend continue today with women staring longingly at designer shoes, fawning over limited-edition jewelry and above all, chasing after already spoken-for men. Be it human or handbag, the more tantalizingly out of reach it is, the more appealing it becomes.

Women think taken men are safe
Women, at least those in good stead with the girlfriend, have the green light to pick the brain of a taken man. They can discuss their romantic strategies, seek advice and flirt without fear of repercussion. A guy who is off the market is, after all, harmless. We know how this movie ends though. Before long, she has fallen for him. Her infatuation comes to light in a moment of devastating clarity. When she’s not supposed to, she far outdoes the girlfriend (“Box seats at Yankee Stadium -- you shouldn’t have!”), at which point the gig is up. Lo and behold, the safety of his relationship status is what lured her in all along.

Women hear good things about taken men
Significant others are a reflection of the people they date. That’s why it’s in a girl’s best interest to act like her boyfriend’s PR rep: to mention whenever possible that he studied at Harvard -- oh, and he plays in a band. When she boasts, her listeners see him through the rose-colored glasses that she wears. By the time she gets to the part about his volunteer firefighting, it’s obvious that he’s a major stud and consequently, she’s his female equivalent. Unfortunately, the girls, now in agreement, want to steal her title away.

Too many women have gotten past the clamor of insincere compliments, kind gestures and sweet nothings only to find a broken record playing at a single man’s core. It repeats, “get some.” Thus, the most well-intentioned actions of single men still have women scrutinizing between the lines. Men who are in a relationship (and respectful of that commitment) don’t use women as a means to an end. Once they settle into something serious, their behavior undergoes purification and the selfish sexual intentions are removed. In turn, women lower their guard.

Women like what is popular
This one is fairly straightforward. Girls want what other girls have. To women, the simple fact that a guy is someone’s favorite flavor makes him worth a try. A guy in a relationship is wanted by at least one person -- the girl on his arm, who confirms that he has been tested and approved as boyfriend material -- and therefore attracts the buzz of many others.

More reasons why single women want you now that you're taken after the jump...

Women want an ego boost
Man or woman, the ultimate ego boost is the knowledge that you’re not just hot, but irresistibly hot. Consider this: If a man risks his entire relationship -- commitment be damned -- for one exceptionally steamy night with another woman, that other woman will go home feeling like she has one-upped Helen of Troy. That’s bragging rights to the max. A shot of confidence like that could make up for a long dry spell of celibacy or jump-start a love life. Plus, if she’s unable to win him over, there’s a net to catch her: “Of course he’s not interested in me; he’s in a relationship.”

Women see taken men as having desirable qualities
To help you further understand how women perceive the dating pool, think of men like parking spaces surrounding a popular restaurant on a Friday evening. The best ones, meaning the ones closest to the restaurant, will be occupied almost solidly until closing. But as one gets farther from the front door, the parking spots aren’t as good, so they open up with greater regularity or, in some cases, remain open permanently. In short, women believe that men who are single are single for a reason. Backward as it may sound, the ones who aren’t available are the ones worth going for.

Women like a challenge
Women who demonstrate the right combination of warmth and affection can bag a single guy like candy on Halloween. Taken men, on the other hand, are tougher to get. For starters, they’re probably content with their current girlfriend and not too keen on gambling that relationship. You’d think this would deter an aggressive girl, but no. With two hearts that stand to gain (and only one to be crushed as collateral damage), the stakes are too high to back out. Also, what if he’s not as happy as he looks? Women know a man loves to be fought over, and there’s potential that his girlfriend under-delivers. Hello window of opportunity!

Women want to screw over other women
Then there are those women who simply have it out for their own gender. In grade school, they pulled pigtails; now that they’re older, they pull boyfriends. Some are out for revenge, others make a sport of seeing if they “can get him,” whatever the emotional cost. Women size up their competition and somehow rationalize that her boyfriend is begging to be with a real woman -- no offense to the tramp he’s with. Remember, too, that women aren’t always down with waiting patiently for a taken man to free up. They want results, and they want them yesterday.

Taken men have confidence
The next time you go out, take a look around. The most confident guy in the room isn’t the one usurping attention or emptying his wallet on drinks for the gang. The man exuding confidence like perspiration in a sweat lodge has his arm blissfully around his bombshell of a girlfriend -- and in case you didn’t notice, she’s all about him. What better proof exists that he is successful, intelligent and endlessly charming? Men who enjoy this luxury are infinitely more natural, comfortable and cool. They worry little, stress out even less. This all adds up to a man with incredible romantic gravity who pulls women into his orbit.

http://m.askmen.com/top_10/dating_200/213_why-do-single-women-like-taken-men.html