If I remember correctly the Sarah event in the original was not NTR since the MC and her were not officially together when it happened. That was the point, to pursue her and convince her that you wanted the relationship. If you fail and she ends up with the other guy well, that's called failing and it's normal to happen sometimes.
In this version, however, it seems there might be a real possibility that either her or Rachel get fucked by Christian, willingly or unwillingly, after they are already together with MC. Now that's NTR and it's gonna lose him patrons big time. Yes, there are people who are into that but there are far more who HATE it.
As for the story, it went sideways long before the last update of the original. The sisters were lobotomized to finish their story easier. Random pointless characters were introduced just to say that there are more sex scenes (Charles's mom, cousin just to name 2) as well as adding gay and futa content for the minority of patrons who voted for that - he even had to dial it back with that since a poll he made pointed out that, surprise!, people did not want the MC to suck dick.
I am disappointed by all this but this is one of the first and most interesting/expansive adult games I've played so I will stick around just to see how it ends.
And who knows, maybe if I have some free time one day I'll take it apart and replace the dialog with my own story. I did this to fix his stupid bugs before and fix some cringy dialogue so maybe (alcohol would be involved)