I found a verse in the Bible that can be used to defend homosexuality: "And above all things have fervent love for one another, for "love will cover a multitude of sins" (I Peter 4:8). In other words, even if it is a sin, the love of these two people for each other completely destroys any of that. In other words, the sin is overruled by the love.
"Cover" translates the Greek word kalupto, which means to conceal or hide. Love for a brother leads you to help him out of sin, so that he may have forgiveness from God. "Brethren, if anyone among you wanders from the truth, and someone turns him back, let him know that he who turns a sinner from the error of his way will save a soul from death and cover a multitude of sins" (James 5:19-20).
Love also means you understand his embarrassment at sinning, and so you cover up the past -- no longer bringing it up -- so he bear up under the burden. "Brethren, if a man is overtaken in any trespass, you who are spiritual restore such a one in a spirit of gentleness, considering yourself lest you also be tempted. Bear one another's burdens, and so fulfill the law of Christ" (Galatians 6:1-2).
The mistake being made is assuming that the person remains in sin, but that is not what Christianity is about. Sure, all Christians sin, but they seek to leave the sin.
"If we say that we have no sin, we are deceiving ourselves and the truth is not in us. If we confess our sins, He is faithful and righteous to forgive us our sins and to cleanse us from all unrighteousness. If we say that we have not sinned, we make Him a liar and His word is not in us. My little children, I am writing these things to you so that you may not sin. And if anyone sins, we have an Advocate with the Father, Jesus Christ the righteous" (I John 1:8-2:1).
"No one who is born of God practices sin, because His seed abides in him; and he cannot sin, because he is born of God" (I John 3:9).
By "cannot sin" John is saying that he cannot remain in sin. A Christian finds sin abhorrent and will work to leave it. "For a righteous man falls seven times, and rises again, but the wicked stumble in time of calamity" (Proverbs 24:16).
There is no "even if" in regards to whether homosexuality is a sin. See: What kinds of homosexuality does the Bible mention?
Love does not overrule sin. It is because of God's love that a way out of sin has been offered. True love doesn't want sin in a loved ones life. Love "does not rejoice in unrighteousness, but rejoices with the truth" (I Corinthians 13:6).