"Comets Fade with Summer" by Amber Lambda

I didn't know quite what to expect from this book.  A teenage girl is falling in love with her imaginary best friend?  What?  I got it as a gift from a friend who was confident I would like it, and they were right!  I did.
Halley has to move to California right before she starts the next year of high school.  She'd worked so hard to fit in with the coolest girls in her old high school, and now she has to start all over... but how?  She's not actually cool herself, she's just really good at blendi...