In Buddhism, marriage is regarded as entirely a personal and individual concern.
Although monogamy is not regarded as a matter of social convention, the Buddhist layman is advised to have one wife. Although the Buddha has not restricted his followers to one wife, there are sermons he has delivered to show how wise it is to have one wife and not to go after other women. The Buddha says that one of the causes of a man's downfall is to go after other women. Man must realise how difficult it is to maintain even one wife and family. He must realise what would be his position if he tries to have more. Therefore, it is advisable to have one wife. Also, the Buddha very clearly advised his followers to keep away from committing adultery.
The Buddhist views on marriage are very liberal: in Buddhism, marriage is regarded entirely as a personal and individual concern. There are no laws in Buddhism that force a person to marry. Also there are no laws in Buddhism that require a person to remain as a bachelor or to lead a life of total chastity. There are also no laws in Buddhism to require a person to produce children or to regulate the number of children that he produces. Buddhism allows each individual the freedom to decide for himself all the issue pertaining to marriage.
Separation or divorce is not prohibited in Buddhism though the necessity would scarcely arise if the Buddha's injunctions were strictly followed. Man and woman must have liberty to separate if they really cannot agree with each other. Separation is preferable to living a miserable and harmful family life for a long period of time. The Buddha further advises old men not to have young wives as the old and young are unlikely to be compatible and hence will have to suffer greatly.
Taken from "What Buddhists Believe"
Written by Ven. K. Sri Dhammananda
Published by Buddhist Missionary Society