yeah, I agree for the most part, after the kiss in the pool I thought we were already there, but Haley shuts MC down, clearly lying the herself, she contradicts herself sleeping with her brother like that, letting him see her naked, grabbing his dick and so on
but I don't think it doesn't make any sense, she is clearly torn between her desire for her brother and her fear of losing something important for her, she is fearful of what they will become if they cross the line, at the same time she can't stop thinking on her brother, she even scolds him when she goes to that trip with Adriana for not showing her how he missed her.
I don't know exactly what she is afraid to lose when they cross the line, she states that it's "everything", but what exactly? We don't know for sure