Neither of them seemed to have noticed that a fierce battle was raging inside Harry’s brain:
She’s Ron’s sister.
But she’s ditched Dean!
She’s still Ron’s sister.
I’m his best mate!
That’ll make it worse.
If I talked to him first —
He’d hit you.
What if I don’t care?
He’s your best mate!

Harry Potter and the Half-Blood Prince – J.K. Rowling