No, Jesus would not have supported same-sex "marriage" because he clearly reiterated the definition of marriage as found in the Old Testament, that marriage is the lifelong, mutually exclusive union of a man and a woman that is oriented toward the bearing and rearing of children. This has also been the consistent teaching of the Catholic Church throughout its history.
The Scriptural basis for marriage is established in Genesis when God creates the human person—male and female—in His divine image and likeness.
Marriage is an overarching theme of Scripture, which speaks of "its 'mystery,' its institution and the meaning God has given it, its origin and its end" (Catechism, No. 1602).
In fact, the Bible begins and ends with marriage: In Genesis we read of the creation of man and woman in the image and likeness of God (Genesis 1:27), and in Revelation we read of a vision of "the wedding-feast of the Lamb (Revelation 19:7, 9).
The foundation for marriage is established on the sixth day of creation, when God "created man in his image; in the divine image he created him; male and female he created them" (Genesis 1:27). "The vocation to marriage," states the Catholic Catechism, "is written in the very nature of man and woman as they came from the hand of the Creator" (No. 1603).
"The intimate partnership of married life and love has been established by the Creator and qualified by His laws," states Vatican II. "God Himself is the author of matrimony, endowed as it is with various benefits and purposes."
God recognizes that Adam shouldn't be alone, and that he needs a "helper suited to him." That companion is a woman, Eve.
In the second chapter of Genesis, God determined that it wasn't good for Adam for him to be alone, and that he needed a "helper suited to him" (Genesis 2:18).
Msgr. Charles Pope, pastor of Holy Comforter-St. Cyprian parish and popular blogger for the Archdiocese of Washington, noted that a suitable partner for Adam is first and foremost a human, "for none of the animals proved to be suitable for Adam" (Genesis 2:20).
Genesis relates that God took out one of Adam's ribs while he was asleep, and then built "the rib that he had taken from the man into a woman" (Genesis 2: 21-22).
God then presented Eve to Adam, and the latter exclaimed "This one, at last, is bone of my bones and flesh of my flesh; This one shall be called ‘woman,’ for out of man this one has been taken" (Genesis 2:23).
"The suitable partner for Adam was a woman," Msgr. Pope concluded. "God created Eve, a woman, not Steve, a man."
Additionally, the priest noted, "the suitable partner for Adam was one woman. For God did not create Eve and Ellen and Jane and Sue. Hence polygamy is not of God’s design."
While Msgr. Pope acknowledged that "a number of the Old Testament Patriarchs did have more than one wife," he noted as well that "what the Bible reports as a fact does not necessarily imply approval."
"Fact is," he added, "the Bible shows how polygamy always leads to trouble. As Biblical history unfolds, polygamy begins to disappear."
Adam and Eve "become one body," thus entering a lifelong, stable and indissoluble bond.
After God creates Eve out of Adam's rib, the narrator of Genesis comments: "That is why a man leaves his father and mother and clings to his wife, and the two of them become one body."
"To cling means to adhere, to stick like glue," says Msgr. Pope. "Hence, divorce and disunity are not part of God's vision for marriage."
"Husbands and wives are to strive for unity and stability by God’s grace," he adds. "The easy (no-fault) divorce of our culture is hostile to God’s plan for marriage. Couples should not seek easy ways out, they should do the work necessary to preserve union and stability in their commitment of marriage."
The Second Vatican Council states that "a man and a woman, who by their compact of conjugal love 'are no longer two, but one flesh,' render mutual help and service to each other through an intimate union of their persons and of their actions."
"Through this union they experience the meaning of their oneness and attain to it with growing perfection day by day," it added. "As a mutual gift of two persons, this intimate union and the good of the children impose total fidelity on the spouses and argue for an unbreakable oneness between them."
The US bishops' conference reminds us that the union between man and woman in marriage is a "bond that cannot be dissolved by the will of the spouses": "Marriage thus created is a faithful, privileged sphere of intimacy between the spouses that lasts until death."
Children become an essential dimension of marriage when God tells Adam and Eve to be fruitful and multiply.
The first chapter of Genesis ends with God blessing the first man and woman, and saying to them: "Be fertile and multiply" (Genesis 1:28).
From the very beginning, God makes clear that one essential purpose of marriage is the bearing and rearing of children. The Second Vatican Council states that "the institution of matrimony itself and conjugal love are ordained for the procreation and education of children, and find in them their ultimate crown."
"Children are the supreme gift of marriage," it adds. "Without intending to underestimate the other ends of marriage, it must be said that true married love and the family life which flows from it have this end in view: that the spouses would cooperate generously with the love of the Creator and Savior, who through them will in due time increase and enrich his family."
The Catechism notes that even for "spouses to whom God has not granted children can nevertheless have a conjugal life full of meaning, in both human and Christian terms. Their marriage can radiate a fruitfulness of charity, of hospitality, and of sacrifice" (No. 1654).
Jesus reiterates God's plan for marriage as articulated in Genesis and adds, "What God has joined together, no human being must separate."
In Chapter 19 of Matthew's Gospel, Jesus is asked about marriage and the possibility for divorce. Without missing a beat, Jesus replied, "Have you not read that from the beginning the Creator ‘made them male and female’ and said, 'For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh?' So they are no longer two, but one flesh. Therefore, what God has joined together, no human being must separate” (Matthew 19:4-6).
Those questioning pressed further, noting that Moses himself allowed for divorce. Jesus answered with the same clarity: "Because of the hardness of your hearts Moses allowed you to divorce your wives, but from the beginning it was not so. I say to you, whoever divorces his wife (unless the marriage is unlawful) and marries another commits adultery" (Matthew 19:8-9).
In this exchange Jesus is clear about the definition of marriage—that it is between a man and a woman, and that it is an unbreakable bond that not even the spouses themselves can break.
Msgr. Pope interprets the text in this manner: "Jesus does not say a man clings to his partner, rather his 'wife.' Jesus then says with his own authority: 'What God has joined together, let no one separate.' This text surely forbids divorce, but one might also argue a wider interpretation wherein Jesus forbids us to tamper with what God has established."
Pope Leo XIII notes that when reading the Gospel of Matthew, "we see clearly that this doctrine [of marriage] was declared and openly confirmed by the divine authority of Jesus Christ. He bore witness to the Jews and to His Apostles that marriage, from its institution, should exist between two only, that is, between one man and one woman; that of two they are made, so to say, one flesh; and that the marriage bond is by the will of God so closely and strongly made fast that no man may dissolve it or render it asunder."
He continued: "Jesus Christ, who restored our human dignity and who perfected the Mosaic law, applied early in His ministry no little solicitude to the question of marriage. He ennobled the marriage in Cana of Galilee by His presence, and made it memorable by the first of the miracles which he wrought; and for this reason, even from that day forth, it seemed as if the beginning of new holiness had been conferred on human marriages."