Shino88 how attached are you to that optional NTR? cause if you plan to only have a scene or two, it may be better off removing it all together, since people will avoid the game simple cause it has the tag on the thread without checking that it is optional.
And well it kinda does also contrast the whole harem premise (the way you seem to be building up MC in the main image he doesn't seem like someone that would get cucked either).
Not saying you have to though of course, if it is something you want by all means, just thought I would throw that out there if the normal harem-loving audience is your main goal (basically don't stretch yourself too thin to include optional genres/fetishes, may come at the cost of your target audience if not careful).