First of all, let me encourage you to, above all, show the love of Christ. Do not allow yourself to get involved in heated debates. That only brings hurt and anger, which closes doors on the truth. Secondly, do not focus on the behavior. It is not the act of homosexuality that God wants to change. It is the heart that is closed to the truth of God’s Word that needs to be changed. You can convince someone to change his behavior, but that gets him no closer to Heaven. It is the condition of the heart that needs to be changed and then the behaviors will naturally follow.
God Word says that He is powerful and effective even to demolish strongholds (read 2 Corinthians 10). So, point your loved one to the love of Christ through the Word of God and show him that God does not call him to perfect himself before he can come to the cross, but that at the foot of the cross is where Christ will begin His work.
Above all, pray for him constantly and ask God to give you guidance as you reach out in love. James 5:16 states: “The earnest prayer of a righteous man has great power and wonderful results” (TLB).