What keeps people from telling their partners that they are unhappy in the relationship and want to move on to someone else? Is it the etiquette of the thing? Or is it about sparing your partner's feelings? Os is it selfishness? For married couples, is it the expense of the divorce?
If the reason people cheat is not to hurt others, if the wife,husband or girl/boyfriend finds out about it, does it lessen the pain? Isn't it worse? Aside from the pain of the breakup (or the possibility of it), you are dealt with betrayal, humiliation and the rosy mirror you have been looking at thinking that your world is just perfect will be shattered to pieces. Doesn't that multiply the pain to 3 or more?
What about if there are children involved? Regardless of the age, children who grew up in a loving household and looks up to their parents' union will be affected by the knowledge that one parent became unfaithful to the other. Adult children may understand but it will take a while for them to recover nonetheless. It is never easy to have one's rosy mirror shattered and your perception altered.
As for the third party, what keeps you interested in people involved with somebody else? From the posts I've gleaned that it's the connection. And it is difficult to ignore people you have connected to. But I don't think we all get involved in a relationship instantaneously. Nor do we fall in love instantaneously (sorry, don't believe in love at first sight). Isn't there a point where we ask ourselves whether we are going to get involved with somebody or not? When you get to that point, how do you arrive at the conclusion that it is okay to be with that person? Is it because they are so irresistible?
If the husband/wife tells you that their marriage is on the rocks, which is why they are pursuing you, is that really true? Whose perspective is that? Did you talk with the other person and confirm that information for yourself?
Now that you are inlove and involved, what keeps you from breaking things off especially if the other has no sign of breaking up with the other person?
I didn't post this to judge others' actions and decisions. I believe that people have only themselves to answer to for the decisions they have made. My objective is to learn those reasons why this happens.
All opinions welcome. And please no name calling! Let's be adults about this. We may discuss this heatedly but it won't do to resort to childish tactics,

Looking forward to reading other people's point of view...