So, two things I have gathered from this chapter regarding Nanjou's attitude towards sex and relationships.
First, she has never had a normal relationship before, either romantic/sexual OR platonic. People complaining about her being a slut are forgetting that. She basically was a loner introvert right up until high school where she changed her image, and unfortunately drew the attention of guys just looking for an easy lay (which she obliged because of low self-worth due to no confidence). So, she has little to no idea of how to act in a 'normal' relationship, which is why she keeps bringing up sex. It's all she's been taught up to this point.
Secondly, she MIGHT also be using sex as a sort of defense mechanism for unfamiliar situations and feelings. Since it's all she knows, it's the only thing she can 'rely' on. I'm sure we will see less of her just pushing for sex as they develop their relationship.
Looking forward to it.