Now that I understand what NTR is, at least it seems to me. I didn't foresee this happening in the near future.
In any case if it were to happen it would be avoidable due to player choice.
I'd recommend never having it and just getting any idea of it out of your mind now if it is not a focus of the game. If Jason isn't going to end up with a girl because of player action, there is no need to show her having sex with someone else. You should just have her leave the game. At its most basic level, this is what NTR is to most people who don't want to see it: a female character that is, or could be, a love interest for the main character having sex with some other man. Showing it is not needed and it takes away time that could be used making other scenes.
And here's why you should just not show a female character with another male besides Jason if it is not the main focus of the game... Players who like NTR will not be happy with it unless it is a core part of the game, and players who don't like it will not play your game at all if female characters are fucking other guys.
There is almost never a reason to show a love interest having sex with someone other than the main character. It's better to just have a female character that Jason isn't having a relationship with find a reason to leave the game. If NTR shows up halfway into your game people will be very mad and you will not gain any fans of NTR. NTR fans will by that point have already decided not to play your game because it has been out for a while, and it wasn't NTR from the start.
If this is Jason's story, then he should be the only male character seen having sex unless you want to show a bunch of scenes of that kind of content which will attract a very different audience then it seems like you want.
This is just some advice from a fellow storyteller and writer, I mean no offence by it and am just trying to be helpful. Hopefully everything I've said is clear, I know English isn't your first language so I tried to be as clear as I could.