Just sharing my personal experiences, it is easy for any person who is practicing on the spiritual path to experience different types of obstacles on different levels. Without realizing Emptiness of the True Nature of the Self and All Phenomenas and attaining Full Enlightenment, we are still susceptible to experience obstacles and attracted to vices that will hinder us to further progress because we are not yet free from the attachment to the "Ego." As for upholding the No-Drinking precept, it is helpful to protect oneself from engaging in killing, stealing, sexual misconduct, hurting and harming oneself and others. Once One is drunk , one's mind will be drowsy, dull, and cannot be clear-headed or controlled and engage in non-virtuous deeds that will further harm One's practice and others. If any Spiritual Teacher who said that using Sex is to test the students' loyalty or power or to gain further teachings/transmissions/Enlightenment, he /she is not a true teacher. He/she is probably just using Sex for his or her own interest. It is better to beware of this Teacher and keep a healthy distance and check and speak with other genuine Teachers. Thank you.