The Definition of Marriage

I had a very interesting conversation with an old friend of mine. So interesting that in the end, I got so riled up and upset.
See, he believes that people marry to procreate. To have children. Hence, people who do not plan to have children should not marry. He further argued that the reason is because ALL married couples SHOULD bear the "BURDEN" of having kids.
My definition of marriage, on the other hand, is "a union of two people who are in love". To have kids is a bonus but it surely is not the reason to get married.
And having kids may be difficult, but it definitely is not a burden.
Yes, living together is accepted by our present society. But that does not mean that the definition of marriage and people's reason for marrying should be re-defined.
Am I wrong in my belief? Do I have rose-colored glasses on? What is your view of marriage? What were your reasons for marrying or not marrying?