And the saddest fear, comes creeping in
That you never loved me, or her, or anyone, or anything, yeah!

from Taylor Swift – I Knew You Were Trouble Lyrics on Rap Genius

Meaning

She is worried that this boy could be doing this to many other girls which is even more troubling

He may be feigning his love for these girls in order to sleep with them, though he’s never felt any sort of intimacy towards them at all

To help improve the meaning of these lyrics, visit “I Knew You Were Trouble” by Taylor Swift Lyrics and leave a comment on the lyrics box