I commend you for your stand and hope you will never waver from it–whether others understand it or not. No matter what others do, if you are a Christian, God has called you to purity. The Bible tells us "to be self-controlled and pure" (Titus 2:5).
Why does God want us to live this way? Why does He tell us that sex should be reserved for marriage? The reason is because He loves us and knows what is best for us–and promiscuous sex is never in our best interest. For example, someone who has been sexually promiscuous before marriage will almost never be completely trusted by their spouse. Why should their spouse believe it won't happen again? God knows that your marriage will be much happier if your spouse knows you can be trusted.
Make it your goal to grow closer to Christ during your years in college. Ask Him to help you find other Christians on your campus, and then seek out a Bible study or fellowship that will strengthen you spiritually and morally. Ask God also to guide you as you make important decisions about your future.
No, your old friends may not understand your commitment to follow Christ. But pray for them, and ask God to help you explain simply but clearly what Christ means to you. They need Christ's presence in their lives every day, just as much as you do.