Here's one of those "holier than thou" posts...
First off, anyone can cheat, no matter how hot their spouse is. For example, even celebrities with blistering hot spouses have cheated: Eric Benet cheated on Halle Berry, Jude Law cheated on Sienna Miller, Brad Pitt (allegedly) cheated on Jenifer Aniston. And most recently, Tiger Woods cheated on his lovely wife. The list could go on and on.... I doubt if any of these fellows "settled." I'm willing to bet that these men were heavily in love with their women in the beginning--and even during--the time when they cheated, but testosterone is a b***h. Of course, monogamy is quite possible, and is the ideal for many.
Of course, monogamy is quite possible, and is the ideal for many.
Point is, relationships DO get dull every now and then; ask any married couple. And as you pointed out, you can always do things to spice it up. I just find it hard to believe that a man doesn't get to a point where he actually starts to fantasize about other women (not that he EVER has to act on it), which I believe to be quite natural.