It depends on how you interpret NTR because people often have different perspectives on it.
Anyway, in vol 3, Sasha tells Master that she has a Senpai as a sex friend because "It feels good / It's fun," (There's more to it, but just keep it simple) and there are no romantic feelings attached to it. This leads to Master panicking out, then a bit later confessing to her, and Sasha reciprocating his feelings, which leads them to start dating. Then the Senpai sees Sasha and Master going on a date, tries to call Sasha out,
Master tells him to back off, but the dude still tries to be forceful. Sasha then tells him not to interfere, and they proceed to go on their date. This is where the volume ends. (Well, there's another chapter after, but it's just minor stuff).