mc having sex with yui is not NTR though? What is ntr is when other people do it who are not mc. Which is likely as she is being forced to sell herself...
I don't see why you'd advise against it though. It's worse that way for her. If you're the only person she'd actually be semi-okay with, then at least help her out (referencing one specific part here)
Although, I do fully support and respect your decision to boycott the game until she can be saved. (I'm doing the same, lol).
spoiler
I didn't do anything until she begged us to take her virginity before anyone else, did not rent her even once for anything. It didn't feel right. And she is my favorite... That's why I don't see why you'd advise against it and let her be raped and deflowered by some random man instead of who she wants to take her first time (in desperation). Of course, the better option is still dropping.