dear starin2.
you asked what are the reasons behind establishing these sort of illicit affairs. I think these are numerous. I will discuss only a few of them and mainly those concerned with our psyche.
I think feeling of being alone sometimes bring you towards maknig extra martial affairs.
Secondly, May be you woul'nt agree to me in this case but i observed and felt it . Human nature is bascially a restless one .It always wants to quit monotony. Legal marriages contain this factor of repetition. So extra martial affairs are actually , a rebellion and depiction of that basic human instinct. Monotony in any Human relationship affects it and relations demand change and their refreshings after short intervals.
Thirdly, I think Imitation. Media is projecting this sort of trend that establishing these realtionships is not as bad as it used to be . I mean Media is trying to reduce the level of our consciuosness and extent of guilt that stops someone from being astrayed.

Fourthly, your peers, having as many girls as one can simultaneously, do elevate you in the company of your friends. And we all know that girls, the most ever discussed stuff when you are in the company of your friends.
I think I have few others in my mind but i will post them after words. I need suggestions and remarks from all of you . allah hafiz.