Sebastian sees that Aria is exhausted to the point of collapsing. He knows he shouldn't have left her as she was when she stormed out of his office. He should have taken care of her.
Aria doesn't want Sebastian to see her as a weak girl that will give him what he wants when he wants it. He doesn't make it any easier when he leaves groceries in her apartment. She feels used, and like she means nothing.
I like how they get to know each other a little better with mundane facts. One of them may even be fans of a certain boy band. ;) The end of this installment in the serial will have you racing to read the next.