It's possible that she may not have given Tybalt an answer prior to the DnG game and that him seeing her there with him may have led to him reiterating the threat/request because when going on the date, she tells him that she can't see him anymore and that she's been trying to pluck up the courage to tell him this all week, so it would seem that she had accepted it before talking to the MC, the question is when; before or after the DnG game? If it was before then she breached it, not once but twice if she called the MC to come see her in the auditorium, so why we would she not breach it again if she thought she could get away with it?
The expression on her face is what I'm focusing on with regards to who's with her because it's an expression we've seen quite a few times now when the MC is flirty/complimentary to her which is why I think it's him here with her. I can't see her having that reaction to being complimented by Bella or Josy, and if it was that other person, I can only imagine the backlash it would get which is why I don't think it's him either, so that just leaves the MC as the only viable option.