Some more facts to arm yourself against such debates .... A renowned biologist says we are biologically wired for a one-to-one relationship! There is something called imprinting that happens in human beings - once when a child is born, it gets imprinted in its mind that so and so is its mother, the reverse - mother-child imprinting and thirdly during sexual intercourse between two partners(not necessarily the first time it happens). Such imprintings are irreversible processes. This is the reason why he says despite social pressures and even threat of murder,two lovers cannot seperate. There is also another reason for the concept of marriage and relationship. Human babies need long term care and attention than any (or most)other animal. This role can be performed only by the mother, hence the division of work that mother runs the family while the father hunts for food. While in today's world such division is not always required, it has still programmed us to a family relationship. Though a bachelor who cannot vouch for arguments for or against pre-marital sex, I still feel one canlearn and enjoy a lot through committment and trust, in any sphere of life!