Many times when this happens it is because they have an arranged marriage and they need to get married. There are some guys that just don't want to be married and have many affairs and just don't want to settle down. But in some cases, they are forced to by the family because this is their religion or just how it works. They accept the arrange and get married, but in their mind, heart, and soul, they just can be happy with one woman so they have affairs during the marriage.
While other men will fall in love with a woman and want to get married. They want to settle down, but it is hard on them. At first, they don't have an affair, but in the back of their minds, they keep thinking about it. Then one day it just happens. The cycle starts again and they can't stop it. They enjoy and love their wife, but they feel a need to be with other women.