I think in today's world Christians easily get stuck in the mindset that they can't practice purity because they have already had sexual relations with somebody. I want to tell you something different and I hope you understand what I am saying. I have talked to several of my friends about how they feel that they can't practice purity, thinking it is too late for them, but I believe it isn't as simple as that:
It's not too late. It is NEVER too late. Jesus went to the cross for you. He knew everything about you and He loved you so much that He gave his own life so that you could live. He never expected you to be perfect. And Purity does not have to mean virginity. Purity can mean that, "I've had sex, but now I'm choosing to live a God honoring life from now on." Purity has never been just about virginity. Purity is about forgiveness. It's asking for forgiveness from God when we have stumbled and asking Him to help us re-align ourselves with Him. Purity is about having God-honoring relationships and friendships with the opposite sex.
You can mess up and try again; we aren't perfect creatures and we don't have the best self-control at times. But in the midst of our imperfections we have a Father that is full of mercy and love. He wants your whole heart and for you to put your trust in Him so that He can guide you through what is too hard for you to do on your own. God doesn't just want the 'good' parts of you; He wants it all. He wants to heal you and grow you through the struggles and choices we all make.
The point in all of this, is that you do not have to be a virgin to practice purity. Purity is a choice that you can make everyday to honor God. If you repent, your sins are wiped clean and all that is left is following and honoring the Lord.
1 John 1:9, "If we confess our sins, He is faithful and just and will forgive us our sins and purify us from all unrighteousness."