That's one of the favor lines of homosexual marriage advocates. We love our partners, and therefore, we should be allowed to marriage.
That statement may have a superficial appeal, but it's fundamentally flawed understanding of what marriage is all about.
If love was the defining and exclusive consideration of why two people should be allowed to marry there is no reason for preventing a parent and a child to marry. Or two siblings. Or any other range of loving relationships.
Yet we understand these relationships do not constitute a marriage. The same goes for best friends, athletic teammates, coworkers, and neighbors. The list could go on and on. Love can be expressed in these relationships but that doesn't make them a marriage. While love is certainly vitally important to a marriage, it's about much more than that.
Marriage is built on the unique complementary contributions of a man and a woman. They bring unique attributes to a marriage relationship -- things which go beyond love. Not only for their particular relationship but also for the unique fruit of their relationship -- children. A man and a woman are essential for procreation but they also bring their uniqueness together in the raising of their children.
One example, is the importance of a father in the life of a boy. The absence of fathers in the lives of their sons has been enormously destructive for them and society. Males from fatherless households are much more likely to join gangs, do poorly in school and act out in a host of other ways.
A homosexual relationship in a lesbian context precludes a father figure. While a homosexual male relationship precludes a mother.
Yes, love is an essential ingredient in a successful marriage, but a marriage is about much more than just love. Another essential, foundational ingredients are a man and a woman.