If you have another look at the Bible you would see there is no condemnation actually against same-sex marriage. Thankfully a lot of Christians are seeing this now and same-sex unions are at last being made legal. Here, on December 5th, in the United Kingdom, same-sex couples will be able to marry. Also, marriage has changed, maybe not God's original version, but today's marriage is actually a modern invention. Today's version of marriage did not exist 2000 years ago. Why does no one care about that? Same-sex couples were able to marry 2000 years ago, a fact we have tried our best to forget!
You stated: "Today's version of marriage did not exist 2000 years ago" and in this you condemn yourself. The same God who defined marriage remains the same. He defined it as a union between a man and a woman:
"Therefore a man shall leave his father and mother and be joined to his wife, and they shall become one flesh" (Genesis 2:24).
"Yet you say, "For what reason?" Because the LORD has been witness between you and the wife of your youth, with whom you have dealt treacherously; yet she is your companion and your wife by covenant. But did He not make them one, having a remnant of the Spirit? And why one? He seeks godly offspring. Therefore take heed to your spirit, and let none deal treacherously with the wife of his youth" (Malachi 2:14-15).
"And He answered and said to them, "Have you not read that He who made them at the beginning '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 then, they are no longer two but one flesh. Therefore what God has joined together, let not man separate" (Matthew 19:4-6).
The Bible clearly defines marriage as taking place between a man and a woman. The marriage is established by a covenant. And marriages exist, in part, for the purpose of raising godly children. Homosexuals cannot biblically marry, regardless of what foolish men may desire to declare in their laws.
God has not changed. "Jesus Christ is the same yesterday, today, and forever" (Hebrews 13:8). God has forbidden man from altering His word. "I marvel that you are turning away so soon from Him who called you in the grace of Christ, to a different gospel, which is not another; but there are some who trouble you and want to pervert the gospel of Christ. But even if we, or an angel from heaven, preach any other gospel to you than what we have preached to you, let him be accursed. As we have said before, so now I say again, if anyone preaches any other gospel to you than what you have received, let him be accursed" (Galatians 1:6-9). Hence, Christians are to stay the course and not to follow the corrupt whims of the world. "Therefore, brethren, stand fast and hold the traditions which you were taught, whether by word or our epistle" (II Thessalonians 2:15).
Your admission that England's new definition of marriage is not the same as God's original shows your lack of respect for the sanctity of the truth (John 17:17).
God does not give approval to same-sex marriages for the simple reason that homosexuality is a sin. "Do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived. Neither fornicators, nor idolaters, nor adulterers, nor homosexuals, nor sodomites, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners will inherit the kingdom of God. And such were some of you. But you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus and by the Spirit of our God" (I Corinthians 6:9-11). Hence, your statement that homosexual marriages existed 2,000 years ago is false when applied to the Christian community. Even history supports this. Aristides in 125 AD stated, "The Greeks, O King, follow debase practices in intercourse with males, or with mothers, sisters, and daughters. Yet, they, in turn, impute their monstrous impurity to the Christians." Athenagoras in 175 AD stated, "They do not abstain even from males, males with males committing shocking abominations, outraging all the noblest and comeliest bodies in all sorts of ways."
England did not allow homosexual marriages because of Christian acceptance of homosexuality. The laws gained approval because Christianity is being rejected.