It's easy, you just mix ground unicorn horn with water and voila! You can also add it to food. Just remember to add it after cooking as heat reduces the effect.
A sequel is definitively in order for this bad boy. Part of me says he should stop affair and hope he dodged bullet of not being found out but on the other hand, he might want it to continue if the nurse was mind-bended from this incident and he ends the fling, she might follow thru on her "playful" threat on the last page.