Meredith: Why do people cheat?
Derek: That's a good question.
Meredith: Why do you think she cheated on you? Were you different then? Were you a bad husband?
Derek (pauses): I was... ah... I was just a little absent. Not that is an excuse for her.
Meredith: Do you think things would've been different if you'd had kids?
Derek: Do I think she wouldn't have cheated? ... (he shakes his head) I don't know.