You can't stop him or her from pursuing the gay life. You must learn to trust God to draw your loved one by His Spirit. Trust Him to protect your loved one. God's desire is to free homosexually oriented people from sin and deception. Pray, fast, and wait.
Prayer combined with fasting is a powerful spiritual weapon.
Like it or not, it's going to take much prayer and fasting. Jesus knew prayer and fasting got results. He practiced it, as did His disciples. Throughout the Bible, when men and women faced difficult circumstances, they prayed and fasted. God often responded in miraculous ways.