I'm a married man, have been for five years. Dated my wife for five years before that. Occasionally, the thought pops into my head, sex with another woman would be nice. Perhaps I don't consider it quite so casually. Would I like a donut? Would I like to watch TV? Would I like to cheat on my wife?
It is tough to keep the passion aflame when you both come home tired, stressed and just wanting to forget the slog you've been through. And this is without kids and in jobs we both claim to enjoy (or at least find satisfying). It just doesn't and cannot compare to the intensity of a new relationship. So my reptilian brain asks for more woman flesh and I always have to quash it. It's actually not very hard.
1) Getting some other girl pregnant would be terrible.
2) Catching a disease would be worse.
3) Giving that disease to my wife horrifies me.
Sure, you could work it to minimize those risks. T'ain't hard. But it's also true that the only way to be 100% sure is abstinence. There is more to it than the simple high school sex ed routine though. Even if you presented me with a woman who had no uterus and doctor's papers saying she was cleaner than the vacuum of space, I still wouldn't touch her with my ten-foot pole.
I made a promise on my wedding day and I intend to keep it. I have an amazing relationship with my wife; emotional, intellectual and physical. The truth of the matter is that, while my instincts want me to impregnate as many females as possible, the grass is pretty goddamn green on this side of the fence.