Middle Grade book about two girls that drift apart after entering middle school

[Kaley]

I read this book around 2009-2010 when I was in middle school. The book is about two girls that had been best friends most of their lives. When they enter middle school, they start to grow apart. One girl becomes girly and popular, while the other girl is a tomboy that befriends and starts to like a boy she plays basketball with. Book was probably published in the 2000s.. if I remember correctly the cover has 2 girls laying side by side in the grass. At some point in the beginning of the book there is a big sleepover with several of their friends where drama happens. The book has always stuck with me but I have never been able to remember it.

[Rainbowheart]

The Secret Language of Girls?