God is not anti fun, he's anti hurt.

 1 Corinthians 6:15-20

 15.  Do you not know that your bodies are members of Christ himself? Shall I then take the members of Christ and unite them with a prostitute? Never!
 16.  Do you not know that he who unites himself with a prostitute is one with her in body? For it is said, "The two will become one flesh."
 17.  But he who unites himself with the Lord is one with him in spirit.
 18.  Flee from sexual immorality. All other sins a man commits are outside his body, but he who sins sexually sins against his own body.
 19.  Do you not know that your body is a temple of the Holy Spirit, who is in you, whom you have received from God? You are not your own;
 20.  you were bought at a price. Therefore honor God with your body.