After two stabs at it, I'm not sure what to write about this topic. You want to be entertained, not preached at, right?
So… How to make infidelity fun. Hmmm.
Okay, how about this. You know the old 'drunk around the campfire' question: If you could be absolutely sure that you'd never get caught (with babealicious space alien embellishment), would you cheat?
Current estimates (pulled off the internet, so who knows how accurate they are) are that 60% of men and 40% of women cheat. This either means that more men are involved in supposedly committed relationships than are women (assuming het parity, that doesn’t make sense), or there are a few very busy single ladies out there. If everyone were truthful, it seems that the numbers would be about the same.
If we're going to assume that the numbers are low but somewhat accurate, for 40% at least of the population the answer is "Yes, sure, I'd cheat." They apparently don't even need the 'never get caught alien babe' scenario. But let us play around with the 'never get caught alien babe' thing, because it's much more interesting than regular cheaters.
What are the odds that after a light-years long trip, a hot alien babe will stumble off her spaceship insatiably horny? I don’t know about you, but even after a short flight to San Francisco, my first order of business isn't usually to get laid. Airports aren't designed with sex in mind (despite what a former member of the senate and writers of erotic fiction seem to think), so I can see why the alien babe would decide to land somewhere remote instead of JFK or LAX. But remote usually equals few people, so what are the odds that she'll find a remote place to land which also happens to be close to a human who will scratch her itch? Astronomical! But let's assume that she has some sort of 'horny dude in a remote location' finder that gives her the perfect coordinates to land her craft and get some willing action (from a human). She walks off her spaceship ready to do the deed. And there he is, drawn by her landing lights, the perfect horny, 40%, dude who is willing, ready, and able to service her aching need.
Now we hit the thorny problem of alien versus human anatomy. (Reality sucks doesn't it?) (Oh wait, we're talking about horny space chicks.)(Just humor me.)
What if she's hot, but has this dismaying habit of ripping off the male's head during copulation? Dude, if someone finds your decapitated body in a corn field, and your pants are around your ankles, people are going to know that you were getting some space luvin' when the unfortunate 'beheading in the throes of passion' thing happened. That's getting caught.
What if she's made of molten sulfuric gelatin? If you show up at a doctor's office with a melted penis, someone is going to suspect something. You can make up any story you want to. They're going to know that you got some out of town strange, and pray to God that whatever melted your dick isn't a virulent case of space gonorrhea.
What if you lift her tight little mico-miniskirt over her perfect ass only to find out that alien babes have cocks? Huge, bio-luminescent, prehensile cocks. Since a number of het guys secretly, or not so secretly, want buttsex, that may not be a problem. Hey, buttsex and space chick boobs! Who could pass up that? And unless her cock implants an egg that will eventually hatch and burst out of your chest ala Alien, there's a chance that you might possibly be able to do this without getting caught. Except, of course, that you'll spend the rest of your life searching the night sky for flashing lights while your wife pegs you with the MaXXXimus Anal Intruder. In that case, I'd have to say that cheating was totally worth it. I'm sure your wife would agree. She'd probably love her new butt slut.