To All the Boys I've Loved Before by Jenny Han
To get over the boys she's loved, Lara Jean Covey has a method: write each of them a letter and seal it away in a teal hatbox her mother had given her. When the letters are sent out, however, Lara Jean is mortified. One recipient is Peter Kavinsky, who has just broken up with his long-term girlfriend, Gen. Peter and Lara Jean agree to fake date, hoping it will get each other what they want--Peter back with Gen, and Lara Jean hopes to make Josh, the boy next door she's secretly loved for years, jealous. Of course, nothing goes quite according to plan.