NTR is about betrayal, where your partner cheats on you. NTS is the opposite, you actually enjoy watching or knowing your partner is with someone else.
No, NTR is straight up cheating, NTS is more like one-sided swinging. If the husband/bf is aware and has approved, it's not cheating and not NTR. However, many NTS stories do turn into NTR if the woman starts going behind her boyfriend's back
