The production of images and exciting experiences is one of the most common ways in which self-image seeks to avoid Union.
(Gerald May, Will and Spirit)
The Fall in the Bible talks about was about Adam becoming aware of his creative powers, and with it, the potential for mis-creation. While there even may have been masturbation before the Fall, mis-creation arose when Adam became aware of the separate "I". Mis-creation can happen in many ways, but sexually, Adam's erect penis can become the conscious symbol of the separate existence, the symbolic "I" so to speak. In the conscious act of masturbation, man enjoys diverting the cosmic energy away from the vertical testicle - third eye connection, horizontally into nothingness.
Again, the act of masturbation is not the villain here, neither is the physical expression of love. What disconnected us from the Garden of Eden was the conscious departure from Oneness. Yet, the door to the Garden of Eden has always been wide open to return. Oneness is with us every step of the WAY.