Understanding Fornication

Fornication is a general term for sexual sin. Every type of sexual sin falls under the umbrella of fornication. More specifically, masturbation is lasciviousness, which means beyond normal desire. Normal desire is a person desiring the opposite sex. There is a story in Greek mythology that's about a guy falling in love with himself, which is not normal, just like masturbation. I bought a book called The Complete Kuma Sutra translated by Alain Danielou, and it tells why masturbation was done, and the reason was beyond normal desire