I'm very thankful for what God has done in your life - and what He can do for any person who turns to Christ and opens their life to His transforming power. As you've discovered, the Bible's words are true: "Therefore, if anyone is in Christ, he is a new creation; the old has gone, the new has come!" (2 Corinthians 5:17).
Why were you so slow to admit your need of Christ? One reason, I suspect, was pride. Pride makes us think we don't need God, and it also makes us refuse to admit that we're wrong and need to take a different road in life. The Bible says, "In his pride the wicked does not seek him; in all his thoughts there is no room for God" (Psalm 10:4). Pride blinds us to our faults, and keeps us from admitting we need a Savior.
You also may have become a slave to your own habits and pleasures - and these blinded you to your need for God. You convinced yourself that your sinful ways were best, and every other way was dull or empty. But you were wrong. The Bible says, "There is a way that seems right to a man, but in the end it leads to death" (Proverbs 14:12).
Pray for your old friends, and ask God to use you to point them to Christ. They may laugh at you at first, but they can't argue with the reality of a changed life.