I think this is probably another symptom of what was discussed earlier, her loneliness and commitment issues caused by getting uprooted over and over during her childhood. She wants friends, she wants human intimacy, she probably wants love, but at the same time she's afraid of opening up and getting into a deeper relationship with anyone because she expects that it will just go up in smoke once she's forced to move away the next time. So she knee-jerk has sex with Noro because she wants closeness, then she knee-jerk pushes him away because she's afraid of getting hurt, then she feels sad and lonely when she realizes that he's even further away from her than before because she still wants and needs closeness. I also don't think Noro doesn't care, I think he's hurt and avoids her because he doesn't want to be reminded of the pain.