Scene from Adaptation

Charlie: There was this time in high school. I was watching you out the library window. You were talking to Sarah Marsh.
Donald: Oh, God. I was so in love with her.
Charlie: I know. And you were flirting with her. And she was being really sweet to you.
Donald : I remember that.
Charlie : Then, when you walked away, she started making fun of you with Kim Canetti. And it was like they were laughing at *me*. You didn't know at all. You seemed so happy.
Donald: I knew. I heard them.
Charlie: How come you looked so happy?
Donald : I loved Sarah, Charles. It was mine, that love. I owned it. Even Sarah didn't have the right to take it away. I can love whoever I want.
Charlie: But she thought you were pathetic.
Donald: That was her business, not mine. You are what you love, not what loves you. That's what I decided a long time ago.
Donald: Whats up?
Charlie: Thank you.
Donald: For what?