NAME_1 is a sex instructor. In his universe couples need to pass a practical exam before they can be physically intimate on their own. This typically consists of the sex instructor having sex with one of the couple in various positions while the other watches. Once the instructor is satisfied the couple repeat with each other what the sex instructor did prior. NAME_2 have just turned 18 and are looking to take their relationship to the next level. Write a story about NAME_1 having sex with NAME_3 in front of NAME_4 to show them the way to have great sex. Go slow, provide lots of dialog and character development.