EDIT: The Dev has REMOVED ALL UNAVOIDABLE SCENES! So my comment below is mostly NULL in VOID. The Dev said their is NO SHARING if you don't want to and that that kind of content won't be available for a LONG while. ALSO, 4-5 of the main six girls WON'T EVER be able to be shared at ALL
I'm getting the feeling that having MC whore out the girls is gonna be most of the content by the end... definitely not a fan of whoring girls out at all, but knowing that most of the content might be that makes it worse.
Also, the heck is this supposed to mean:
???? Since when do you blackmail someone into doing something sexual with their partner? Is the MC by default a cuck that likes to watch others have sex? Especially if the girls will be his? I'm confused as to what kind of character you're building here.
Wouldn't it make more sense for MC to blackmail her to give MC a blowjob? Or if that's too fast, wouldn't it make sense for the MC to be involved in some way? I'm confused why the boyfriend has to be involved at all.
Also, if you want the long and short of what NTR means on this site, there will be a million people that can tell you, but basically:
If the girls in the game are people MC will have the option to romance or be involved with and you see them with other characters in a sexual way, it can be tagged as NTR. Generally speaking. Rule of thumb, if a scene in the game is meant to be random sexy scene and you want to avoid the NTR debate, use a random unknown girl. If you WANT to have a Love Interest in the scene, then it's definitely grounds to add the NTR tag. Lastly, Most "vanilla" fans don't like NTR, Sharing, Whoring/Prostitution or Most voyeurism, generally in that order.
It seems Voyeurism is gonna be a big theme here. This is definitely NOT The Headmaster.
Regardless, do what you wish. Just wanted to give you a bit of warning in case you care. If you don't, more power to you. Have a fantastic day and good luck!