Hi, I'm MichaelD, and I'm an ass. *crowd mumbles* "hi, michaeld."
Married people do this all the time. It's called "a thing on the side." It's best when it's two married people doing it, because they both don't want anything else (further commitment) and both have a lot to lose...this way they both keep their mouths shut.
Unfortunately, AIDS has done away with the "good old days" of my youth. My old age has also done away with the good old days of my youth. *Sigh* Back then, it was wake up with a burning pee-pee, go get a shot and take monster-horse pills for a week. These days, it's wake up with a burning pee-pee, die about 72 hours later.:Q
But yeah, I would do it (disease worries aside) . As long as both parties agree that it's "for fun." Then nobody losses.