Julia never expected Adam to confront her with such words. Given how possessive he can be of his women, she never thought Adam would even bring this up to her.
Yes, she is fucking someone else, but that someone is none other than her half-sister. Given her beauty and sex appeal, it would be a walk in the park for Julia to find someone else; she was even contemplating it, given how sexually frustrated she had become under Adam's constant provocations, but something inside warned her not to do it.
She felt that if she crossed that line, she would come to regret it later. As for her twisted relationship with her half-sister, she was forced into it, not by her sister, but because of Adam himself.
She needed to find a channel to release all the frustration Adam was making her feel, so the only option she was left with was Hazel.
