Erica M. Chapman 
Teach Me to Forget 

Ellery wants to die. Nothing is going right. Her younger sister is dead, and her family is in a shambles. But on the day that she tries to end it all, even the gun won't work. When she tries to return it, she's intercepted by a security guard who also happens to be a boy in one of her classes, Colter Sawyer. Colter recognizes Ellery's desperation and begins working hard to earn her trust. Why does this cute boy care about my worthless life?, Ellery wonders. But as the story unfolds, it becomes clear that Colter has very good reasons for his vigilance, deep, personal reasons. And whether Ellery likes it or not, he won't let go.