Taylor Swift - Dear John Lyrics Meaning

Traditionally, a breakup letter is called the "Dear John" letter, I suppose in this case, it is a breakup song. This song is about John Mayer, but I don't think the title really has to do with the fact that this song is about him.This song is generally about a boy that Taylor Swift loved and trusted, but he didn't love her back.

Long were the nights when
My days once revolved around you
Counting the footsteps,
Praying the floor won't fall through, again.
And my mother accused me of losing my mind,
But I swore I was fine.

The first 2 lines state that to her, it seems like it was forever ago when she loved him (whoever him is) so much, and she finds it very foolish now that she ever did. This states that she was so in love with him he was the only thing she ever worried about.
(Counting the footsteps....) These 2 lines refer to how she would wait and wait for the moment when he would hurt her again, and pray that it wouldn't happen.
(And my mother accused me....) This states that her mother thought that she was crazy for dating him and hoped that she knew what she was doing and wouldn't get crushed when he broke her heart.

You paint me a blue sky,
Then go back and turn it to grey.
And I lived in you chess game,
But you changed the rules every day.
Wonderin' which version
Of you I might get on the phone, tonight.
Well I stopped picking up
And this song is to let you know why.

(You paint me a blue sky...) Here she is saying that he would make her happy and then ruin things for her.
(I lived in you chess game...Wonderin' which version...) Here she is saying that she thinks she has him all figured out, but then he changes and she doesn't understand him anymore and that she is always trying to figure out what to expect when he does change.
(Well I stopped picking up...) This says that she finally gave up on him and that she realized that he was using her.

Chorus
The chorus is just stating that she understands now that he used her and that he should have known better.

Well maybe it's me
And my blind optimism to blame.
Or maybe it's you and your sick need
To give love then take it away.
And you'll add my name
To your long list of traitors
Who don't understand.
And I'll look back in regret
How I ignored when they said,
"Run as fast as you can".

(Well maybe it's me...) These few lines say that she only thought of the good things about him and she refused to believe that he was a heart breaker.Here it also tells you that he would pretend to love girls, and then he would break up with them.
(And you'll add my name...) These lines just say that he could add her onto the list of girls he broke up with that don't understand why.
(How I'll look back in regret...) Here she tells that her family and friends warned her that he would use her and then break up with her, but she refused to believe them and now regrets ignoring them.

You are an expert at sorry,
And keeping lines blurry.
And never impressed by me
Acing your tests.
All the girls that you run dry,
Have tired lifeless eyes
'cause you burned them out.
But I took your matches,
Before fire could catch me
So don't look now.
I'm shining like fireworks
over your sad empty town.

(You are an expert...) Here she is telling that he is an expert at breaking up with girls and making sure they don't understand.
(And never impressed by me...) This is the part that I think gives away the fact that he used her. He got her to do work for him but he was never impressed.
(All the girls that you...) She is talking about him breaking up with so many girls, and all the tears that they cried and how they will never be fully healed.
(But I took your matches...) This says that she escaped before he could hurt her to an incredible amount. Now she finds that she has power over him and he is now weak and alone.

I think the Chorus is pretty self-explanatory, so I am not going to write out the meaning of it.
I hope that you now understand this song! :-)