For long it has been said that men pathologically promiscuous and most are always ready for extramarital relationships. Well, this may not be entirely true for all men but many of the male sex are promiscuous - it is said. There are a lot of theories on this and a lot of research is being carried out on the issue by psychologists and biologists.
Biologists, yes, if it is pathological then biologists have better chance of decoding it and they have found one clue ! Scientists have recently found a gene - AVPR1a, which governs a receptor that regulates the production of a hormone called vasopressin produced by brain and this hormone contributes to attachment behaviour with mates and offspring.
My source of the above is www.sciencemag.org which has the following article. I express my thanks to the scientists who have found out this research and the people of sciencemag.org to publish it. You can find the article with complete text here:
Please read the entire article as it shows good insight into the matter.