The Catechism of the Catholic Church: 

1601 “The matrimonial covenant, by which a man and a woman establish between themselves a partnership of the whole of life, is by its nature ordered toward the good of the spouses and the procreation and education of offspring; this covenant between baptized persons has been raised by Christ the Lord to the dignity of a sacrament.”

. . . .

1603 “The intimate community of life and love which constitutes the married state has been established by the Creator and endowed by him with its own proper laws. . . . God himself is the author of marriage.” The vocation to marriage is written in the very nature of man and woman as they came from the hand of the Creator. Marriage is not a purely human institution despite the many variations it may have undergone through the centuries in different cultures, social structures, and spiritual attitudes. These differences should not cause us to forget its common and permanent characteristics. Although the dignity of this institution is not transparent everywhere with the same clarity, some sense of the greatness of the matrimonial union exists in all cultures. “The well-being of the individual person and of both human and Christian society is closely bound up with the healthy state of conjugal and family life.”. . . .

1605 Holy Scripture affirms that man and woman were created for one another: “It is not good that the man should be alone.” The woman, “flesh of his flesh,” his equal, his nearest in all things, is given to him by God as a “helpmate”; she thus represents God from whom comes our help. “Therefore a man leaves his father and his mother and cleaves to his wife, and they become one flesh.” The Lord himself shows that this signifies an unbreakable union of their two lives by recalling what the plan of the Creator had been “in the beginning”: “So they are no longer two, but one flesh.”

. . . . 

2357 Homosexuality refers to relations between men or between women who experience an exclusive or predominant sexual attraction toward persons of the same sex. It has taken a great variety of forms through the centuries and in different cultures. Its psychological genesis remains largely unexplained. Basing itself on Sacred Scripture, which presents homosexual acts as acts of grave depravity, tradition has always declared that “homosexual acts are intrinsically disordered.” They are contrary to the natural law. They close the sexual act to the gift of life. They do not proceed from a genuine affective and sexual complementarity. Under no circumstance can they be approved.

Mayor Giuliani’s position:

“I’m in favor of . . . civil unions,” The O’Reily Factor (Febraury 2004)

“I’m pro-gay rights,” CNN’s “Inside Politics” (December 2, 1999)

“Giuliani opposes gay marriage and has stated that “marriage should be between a man and a woman. He does not, however, support a federal amendment banning gay marriage. As mayor, he signed legislation recognizing domestic partnerships, marched in gay pride parades, actively supported gay rights and temporarily lived with a gay couple during his divorce,” The Pew Forum on Religion and Public Life

“In 1998, as mayor of New York City, Mr. Giuliani signed into law a domestic partnership bill that a gay rights group, the Empire State Pride Agenda, hailed as setting ‘a new national benchmark for domestic partner recognition,’” New York Sun (April 27, 2007).