I’m totally convinced this song is dedicated to Britney. I mean the lyrics are clearly telling us that he’s still isn’t done digging up the past.

"It's breaking my heart to watch you run around
'Cause I know that you're living a lie."
"You said that you were moving on now,
and maybe I should do the same.
Funny thing about that is
I was ready to give you my name."

Looks like he was gonna propose something. Britney would be so much better of with Justin. Still not convinced? Wait, there is more:

"You spend your nights alone,
and he never comes home.
And every time you call him
All you get's a busy tone."