Dear Adam by Kelsey Whitney:
 
Aly and Adam Bloomington have been best friends since birth. They are twins after all. When Adam travels to California for work and to visit an old friend, he leaves his beloved–and ill-behaved–dachshund, Pretzel, behind with Aly.

When Adam FaceTimes Aly, his childhood best friend Levi hovering over his shoulder, Aly can’t believe this tall, broad-shouldered, chiseled stranger is the same scrawny, floppy-haired boy they grew up with. Could this be the same boy she secretly used to crush on? Aly finds herself wanting to get to know the mysterious man he’s grown into after not seeing or hearing from him in nearly ten years.

But Aly’s life changes in an instant when Adam gets in a terrible car crash that leaves him in a coma.

Forced to cope without her built-in best friend, she does the only thing she can think she begins texting Adam about all the things he’s missing, giving him an easy way to catch up when he eventually wakes.

There’s just one Adam’s phone isn’t where it’s supposed to be…