She liked when he decided not to drink because he noticed it made her uncomfortable.
It was probably, more than anything, that she suddenly wasn't another person in a world of people. Not to him. And it felt nice to finally be noticed, especially by someone who continued to surprise her.
It would've felt even nicer if Marley knew she could trust him not to walk away. She would've been more blissful than nervous at the prospect of getting closer to Aiden if she knew it wasn't futile. To the becoming of a friendship with someone who already seemed to understand her well and accept her for who she is.