I've finished the update
Summary of the update based on the play and script:
What happens in the scene with Nicole and the other man depends on whether you chose to share her or go for FFM earlier
If you selected FFM and she has had a drink, the other man will place his hand on Nicole's waist, but she quickly stops him, and the following dialogue occurs:
But just as I was about to step in, Nicole raised her hand and stopped the man. She smiled faintly and said something to him. The man stepped back
If you selected FFM and she hasn't drunk, Nicole won't even let the other man's hand touch her back
If you're in the "sharing" path (Part C), Nicole's mindset changes. The dialogues between MC and Nicole likely happened the night before.
if she hasn't drunk, the kissing scene will happen
If she has drunk, a kiss happens, and the other man grabs Nicole's breasts, but nothing else occurs
It got a bit complicated, as others have mentioned; we need Nicole's point of view. Did she see us at that moment, or what's the situation?
Why does Nicole allow the other man to kiss her in the sharing path but not in the FFM path? The only logical explanation is that, based on an earlier choice, MC and Nicole had a conversation the night before that we didn’t see
Update:
Nicole has definitely seen MC! Because when I set all the cuckoldry stats, anger, etc., to zero but still follow the sharing path, the kissing scene still occurs. Since Netorare is avoidable, that scene cannot be considered cheating—So Nicole saw him and is responding based on his feelings