Your ideas of ntr may be a bit off though.
NTR is all about rubbing it in your face, taunting, stealing.
Also her job is technically a whore.
You don't think every dude she will do in the future because of her job will count as ntr just because it's not mc she is fucking, do you?
The relationship she has with mc feels like an open one, which is fine by me.
But i guess since mc is her master she will need permission from him to do other dudes first, but none of this is ntr.
It's sharing, pretty much.