The tree overlooking the football field.  The orange hair tie.  Englisch.  The Outsiders.  Bus rides.  Hand sanitizer.

They all reminded her of him.  How he made her heart jump, stomach squirm, mouth twitch into a smile at the thought of him.  How her heart twisted and fell when he made eye contact.  His nerdy jokes and fear of germs.  How whenever she was around him, she couldn't be anyone but herself.  Anything but real.  How he knew her so well, no one else could see her inner emotions, but he read her like a book.  How when she couldn't see past her own shortcomings, he talked to her and she felt like the most special girl in the world.  How he chose her, out of all the pretty, smart, confident girls.
How:
he texted her puns, and she was the only one who ever laughed. 
he told her his greatest secret.
he put his arm around her on Halloween, and avoided her afterwards for fear of making her uncomfortable.
he worried about her being the one to stop liking him.
he helped her discover what, exactly, was wrong.
How his hair stuck to his face from his morning shower.
How he told her she was good enough. 
How he asked about how she was doing, his hair falling into his eyes as his brows furrowed with concern.

They reminded her of how, after a long and slow decline, he unknowingly stole her heart, and with it, everything about who she was.
Then destroyed it.