You don't just say:
You see that boy there, the Boy Who Lived? I'm going to marry him one day.
No.
You don't say it.
But you might just think it quietly to yourself for five years.
Until you're suddenly kissing him and he's kissing you back.
And then you might say to your mum one day:
You know the Boy Who Lived? I'm going to marry him.
Because he asked you yesterday.
And you said Yes.
