Are we all looking for the same things?

I've been working on an idea for a new story. The premise is that two people - each married to someone else - are looking for someone to satisfy what's missing in their existing relationships. They meet through an online ad.

So, to do some research, I've been reading online ads for married people who are looking. It became quickly apparent that everyone is basically looking for the same things...sex (obviously) in new/exciting ways, and someone who will help them recapture that feeling of being newly in love/lust, that excitement and anticipation. I'll admit - I miss those things, too. So why is it, then, that we aren't able to get this from our current partners? Why do people have to resort to looking elsewhere? Many are also quick to note that they do not want to replace or leave their current relationship - just find someone who can provide the missing elements and enable them, I guess, to stay where they are.

What would happen if everyone were granted three free passes a year when they got married? Each pass would entitle the user to one no-strings-attached encounter that was not up for discussion with your partner. You choose when to use it, who to use it with, and why. The same goes for your partner. Would that be enough to keep people happy?

Me - I like NSA sex. But I also prefer to have some sort of relationship with the person - as in, we're friends w/ benefits, I guess. I don't like the idea of picking up someone online, or at a bar, or whatever. And that could, I suppose, complicate things if I were in a "3 passes/year" relationship, because jealousy exists in everyone to some degree.

What do you think? Are we all just looking for the same thing? If so, why can't we be content with what we have at home, and work on bringing back the excitement and newness that has dulled over time, due to familiarity or family or whathaveyou? Or is it better to try to satisfy those occasional needs outside the relationship, in the interest of not rocking the boat?