Any sexual activity outside of God’s design for sex is a sin. God designed sex to be a physical and spiritual bond between a man and a woman who are married to one another (see Genesis 2:24). You can read our denomination’s statement specifically on homosexuality here.
How we interact with those who practice any kind of sexual sin depends on various circumstances too numerous to recount here. We should, however, always be guided by the balance of truth and grace.
It’s not necessary, for instance, to “correct” the behavior of those who do not follow Jesus. Jesus came to save sinners (Luke 5:32), and Paul did not judge those outside the church (1 Corinthians 5:12). Scripture teaches, however, that after a person is saved by God and decides to follow Christ they become a new creation and the Holy Spirit makes their spirit responsive and aware of God. Jesus followers want to follow Jesus rather than live in a pattern of sin. (See Romans 8: 1-17).
When someone who follows Jesus is caught in a sin, Scripture tells those who are spiritual to restore them gently (Gal 6:1). Restoration entails bringing them back into fellowship with God and other Jesus followers by teaching truth and encouraging them to live it.