Stefan has left an entry in Elena's diary that shatters her world.
My darling Elena,
I knew you would look here sooner or later. You're able to take care of yourself now, and I've never seen a stronger or more independent girl..
And that means it's time for me to go. I can't stay any longer without turning you into a vampire again - something that we both know can't happen.
Please forgive me. Please forget me. Oh, love, I don't want to go, but I have to.
If you need help, I've gotten Damon to give his word to protect you. Whatever mischief is going on in Fell's Church won't dare touch you with him around.
I'll always love you...