Can I have sex if I am a single Christian?
God is looking for holy people. Christian mates who will not destroy his temple by giving themselves to multiple partners. "Do you know that you are a temple of God and that the Spirit of God dwells in you. If any man destroys the temple of God, God will destroy him, for the temple of God is holy and that is what you are." I Cor. 3:16.
The bible tells us to flee fornication. Keep your temple clean and look for others who are doing the same. The Lord understands that you are flesh and have weaknesses. Nevertheless, He does not want you to be used and abused by others who care only to take advantage of you. God desires that you find a mate who will not just serve you with their body, but physically, mentally, socially, financially and spiritually. He wants you to have the "total package. This is why He ordained marriage. Therefore, that one person can get the whole package. It is better to receive the total package, then receive just ¼ of it!