Hi Notek,
You asked why married men would want to watch others do it when they can do the real thing. I think trying613 has a couple things right: sexual needs and desires are different, and tiavah comes from H' -- it's something inherent to people. It may seem obvious, but surprise, surprise, your wife isn't going to want to have sex every moment that you do. And, surprise, surprise, that "urge" isn't necessarily going to go away just because you're having sex a couple times a week (hopefully). And (last surprise) you'll still have that urge in moments when you're not able to be with your wife: traveling, niddah, heck--being at work.
I hope I'm not coming across as preachy--these are my experiences I'm talking about.
I also couldn't stand the pain of that urge; the sensation of feeling like I needed release. I'm just talking about the physical sensation here--not the mental urge/need/desire. What has worked for me is giving that urge some attention. Focusing on it and really feeling what kind of sensation it is, or how it compares to other physical sensations. Sitting and paying attention to how bad it is compared to other types of pain. Does it feel like a needle in the arm? Hitting your funny bone? For me, I realized that it was roughly comparable to a day-old bruise. Like getting hit hard by a baseball on your thigh. A bad bruise, certainly sore, but still just a bruise.
Man. Just a bruise? It felt so much more intense than a bruise, I had a hard time believing myself. But by actually sitting still, and paying attention to that sensation for a good 5 or 10 or 15 minutes, I started have perspective on the urge/pain. That means that nowadays I can have that urge, that sensation--I have it right now--and be aware of it, and remind myself that it is just a "bruise," it's just sore; I can handle it.
It took some time to get there, and I'm only just starting my shmiras eineyem journey seriously now, but you can do this too.
Lastly, why is it so bad? Our urges--since the physical part, once in perspective, is managable--why are they so bad? Well, I think that's the hard part. The mental/psychological/spritual aspects of urge are the harder things to conquor. But that's another conversation. Sorry this ran on so long. B'Hatzlacha & a chag kosher v'sameach.