Infidelity

What drives people to be unfaithful? A sinful nature or just plain boredom? Despite that infidelity is all around us and that we all experience it in one-way or another, all cases are different. Every couple finds another explanation for betrayal. But two basic reasons would be boredom and unhappiness. People get bored of their partner in life, they feel constrained and lifeless. They might also lack the simple joy of having a spouse or a life partner, they start longing for something more and so they take their first step on the road to infidelity. But despite the cause we usually have the same effect. Either an end of the relationship or its continuation, which is even more unhappy because neither of the partners trusts each other.
Countless books have been written where main events revolve around the act of infidelity. The act of betrayal has been used to produce both comical and dramatical pieces of literature and film. Our views on whether it is excusable or not to commit infidelity may differ, but one thing is certain. Infidelity has been a part of our lives in the past and likely will be joining us in the future.

http://www.allaboutlifechallenges.org/marital-infidelity.htm - A link with some interesting facts on marital infidelity.