Well, she has avoided answering that question to the MC. The way I see it, maybe she is doing that bcoz she didn't sleep with John who is her husband but is having an affair with the MC..she might be feeling guilty. She hesitates to even kiss her husband, there is no way she willingly slept with John. Even in this chapter when John made her kiss his cheek, she ran off somewhere rubbing her lips. When the MC directly asks whether she slept with John, she gets furious. Now you can always say that John might have forced himself on her, but something like that would have been a lot more traumatic. She would not be calling John 'darling', she wouldn't care if John left his suitcase before going to a meeting and she herself would not have attended that school event, basically she would have been traumatized. Not to forget that she sleeps with the MC on the same bed, the very next day. Also, the dev gave the option to avoid NTR with Chloe, who is a side character, I highly doubt he going to force this with Nicole, considering what he said in the past.