“It slowly turned, you let me burn
And now, we're ashes on the ground”

Miley Cyrus – Wrecking Ball Lyrics on LyricsMode
EXPLANATION
Quite hard to make out, but she's saying as he got more popular and famous, his personality towards them and her changed and they're relationship began to flame, ultimately ending in flames.
EXPLANATION
Instead of staying together and supporting eachother, he threw her to the end of his to-do list and didn't care anymore. Now, after what he did they can't come back.
EXPLANATION
He used her for fame and now he left her behind.