Sidebar: I am not referring to that producer/former Studio executive who is clearly a pathological criminal.
I'm taken aback at the scores of husbands, boyfriends, so-called committed partners, and there are the women too, who do not find that their relationship is enough. So, to what can we attribute this: stupidity (not appreciating what they have), peer pressure, narcissism, feelings of inferiority? IMHO, I believe it comes down to respecting your partner, and honoring your own commitments and values. If you believe fooling-around is ok, everyone does it, what harm does it cause, well, then, that's your value. If you believe staying true to your values, honoring your partner with loyalty, love and lasting-power, then that's your value.
I realize that I'm writing in generalizations, but it's a good start for all of us to take a good look at who we are, what we stand for, and how we want to be known. Personally, I think that gravestones should include philandering, cheating, womanizer, etc. as part of the epitaph.