"Christianity says that homosexual sex is "detestable," "unnatural" and "shameful." (Romans 1:27)."
Jesus is the Messiah of the Old Testament which makes it clear that the sin in Sodom & Gomorrah (Gen 19:1-29) was rampant homosexual immorality. Gay men even forcing themselves on unwilling men to perform gay sex with them, and against their will at that. So it was not just gay sex it was gay rape.
Leviticus 18:22 says to men: "Do not have sex with a man as one does a woman; that is detestable."
"Or do you not know that the unrighteous will not inherit the kingdom of God? Do not be deceived: neither the sexually immoral, nor idolators, nor adulterers, nor men who practice homosexuality, nor thieves, nor the greedy, nor drunkards, nor revilers, nor swindlers will inherit the kingdom of God (1 Corinthians 6:9–10).
"For you may be sure of this, that everyone who is sexually immoral or impure...has no inheritance in the kingdom of Christ and God. Let no one deceive you with empty words, for because of these things the wrath of God comes upon the sons of disobedience (Ephesians 5:3–6).
Jesus made it clear what marriage really is and what it is not: “Haven’t you read,” he replied, “that at the beginning the Creator ‘made them male and female,’ and said, ‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh’? So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate.” (Matthew 19:4-6).