Little Black Box by Cindy R. Wilson

I’m not a real doctor but I play one at school. All my patients have to do is fill out the symptom sheet hanging on an empty locker and slide their problems inside. The solution follows in a little black box—mysterious, anonymous, and bearing a personalized cure: music, books, movies…even cupcakes. After all, I’ve suffered enough of life’s symptoms to know the remedies. My mom abandoned me, I’m crushing on a guy who barely knows I exist, and the only person who’ll give me any advice is my father’s boyfriend.
But there are some things music and cupcakes can’t fix. My father’s cancer, for one. And since my own problems are too big to fit neatly in a package, I devise cures for my classmates instead. It seems to be working until I get a symptom sheet from my best friend—one which reveals she’s secretly dating the boy I’ve been in love with since freshman year. That’s when I decide to write my own prescription: for revenge.
I get help from my neighbor, Luke. He’s the only person who knows about my alter-ego. At first, revenge feels good, but then the wrong person gets hurt. Betraying people isn’t solving anything, and worse, it’s putting more than a fence between me and Luke. Now I have to face the consequences of my own little black box and mend my relationship with Luke—especially when I realize I’m showing major symptoms of love.