It was include in the latest update just progress and you will see it :(
Viewing post in Succubus Trick: Grown Up Problem comments
Go to f95zone there is an explanation about NTR this is a comment from there: Just played the game for the first time today and yeah it's definitely NTR lmao the succubus fucks your girlfriend in front of you and sucks on her tits. You can use meme lore like "she used your dick because magic" but it doesn't change the fact she literally fucks your girlfriend in front of you.
I don't like to discuss so let's end this, the content is already deleted so let's no talk more about it, but you are confused with the definition of a harem. So I leave this for you to read. HAREM = 1 Man dating multiple girls at once
POLY(polyamory) = Everyone dating each other
GIRLS FUCKING EACHOTHER? NOT A HAREM
GIRLS FUCKING WITHOUT MC? NOT A HAREM
Well, the truth is, I don't know why they deleted it, but I can tell you that practically what you say confirms it, because for it to be NTR, the context should be given that they are taking it from them, but it is not the situation, at least the content I would have the cheating one, but not the NTR one, because the 3 are literally having it at the same time with the issue that they are separating the MC part, without the context it would be NTR, that is what I want to get to, therefore they are not meeting separating from the main target