Gossip Girl, Season 1

Blair:
What happened? What's wrong? Talk to me.

Serena:
[Serena starts crying] I can't.

Blair:
Of course you can.

Serena:
[sobbing] No, no, B, this is the one thing I can't tell you. I can't tell anyone.

Blair:
I'm not anyone. I'm me, you can tell me anything.

Serena:
[sobbing] No I can't, because then you'll be a part of this and I can't let you be a part of this.

Blair:
What are you talking about? You're starting to scare me.

[Serena sobbing]

Blair:
Hey, hey, hey, we're sisters. You're my family. What is you is me. There's nothing that you could ever say to make me let go. I love you.

[Serena still crying tries not to answer the question]

Blair:
What is it?

Serena:
I killed someone.

[Serena stops crying and stares at Blair. Blair is staring back at Serena shocked as ever]