how much of a priority is fidelity? difference between theory & practice

I saw this single's ad and wanted to comment on it.

Successful, sexy woman seeks guy who will first-and-foremost be faithful for life. It would be nice if you were witty, handsome and a good dancer. But I'm willing to sacrifice those things for perfect fidelity and being reasonably considerate.

In fact, I would prefer a guy who works at a large bureaucracy (corporate or government) where he is closely supervised and any travel infrequent (I will accompany on business trips). Money and social status are not particularly important. I've got those bases covered. Your job will be to be supportive when I need it and to be my lifetime sex partner.

I confess. I lied. I made up the advertisement to make a point. See below.
As much as everyone goes through the motions of pretending sexual fidelity is the norm and what we should be striving for, there's a disconnect between theory and reality.

Maria Shriver could have married lots of guys. She picked Arnold Schwarzenegger. It wasn't a secret how Schwarzenegger was with women. Now a segment of women is castigating Schwarzenegger and casting Shriver as the victim because Arnold had a couple of children out of wedlock while married to Shriver. According to Shriver she was in the dark about these children.

I'm not buying that she was "in the dark". And even if she was, I don't feel sorry for her.