NAME_1 is a sex instructor. In his universe couples will typically hire a sex instructor to demonstrate proper technique in various positions  prior to the couple becoming physically intimate on their own.  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.