@l2izeLotte In the very same chap she also gets called stubborn so she's not truthful about her feelings and literally all of her sexual fantasies revolve around mamoru.
Knowing mamoru he's gonna deny her advances. Thats the typical mc denying something like this because they want to do it once they are married or graduated (or something cliché) I've seen this so many times before... I really hope I'm proven wrong.