You'll quickly find that the one thing people fear most is the idea that they aren't the harem protagonist of their dreams. Example: I moderated in Studio FOW's discord channel. They're busy making Subverse, a kickstarter-backed space RPG smut game. There are 10 ladies in the game to romance, but they'll also sate themselves with the mantics (monsters the scientist chick makes as support units in combat) when they feel like fucking.
This led to hundreds of comments complaining and fearing of being 'cucked', despite us clearing explaining that A) cucking would imply the Captain (the player character) isn't aware of it. He is. If anything its just more fap material for him. B) its entirely consensual, the ladies are doing it of their own free will. The universe Subverse takes place in outlawed sexual deviance, so they're effectively defying an empire by being open with their sexuality. And C) THE SCENES TO VIEW WITH MANTICS ARE ENTIRELY OPTIONAL TO UNLOCK AND VIEW.
It was tiring, and eventually one of the staff just put their foot down on the entire topic. But yeah...trust me when I say the mere idea that anyone could possibly lay with a virtual girl that isn't you in your mind...they will go nuts.