Cheating is the number one cause of the breakdown of any relationship and is probably the most dreaded thing that anyone would dream of happening to them. The fear of a partner cheating and all the trust and jealousy issues that arise because of it is another main reason why relationships falter. So why do people do it? What causes people to put so much time and emotional effort into a monogamous relationship, only for them to throw it away for an affair or one-time dalliance? Here we will look at three of the most common factors that can cause a partner to stray.