LIFELONG - Although divorce is permissible.
To support one another in a lifelong, loving relationship ('They become like garments for one another' - Surah 2)
To fulfil a religious responsibility ('Marry those among you who are single' - Surah 24)
To procreate and start a family (Seen as a duty; reproduction is a gift from God).
To provide stability to society ('The only way to protect all people is to maintain a society where only a man and his wife share the act of sex' - Abdul Wahid Hamid).