Casablanca (1942)

Continuity mistake: In the final scenes at the airport, when Rick is talking to Major Strasser, the epaulettes on Strasser's shoulders alternately appear and disappear. (01:40:05)

Rick: I'm saying it because it's true. Inside of us, we both know you belong with Victor. You're part of his work, the thing that keeps him going. If that plane leaves the ground and you're not with him, you'll regret it. Maybe not today. Maybe not tomorrow, but soon and for the rest of your life.
Ilsa: But what about us?
Rick: We'll always have Paris. We didn't have, we, we lost it until you came to Casablanca. We got it back last night.
Ilsa: When I said I would never leave you.
Rick: And you never will. But I've got a job to do, too. Where I'm going, you can't follow. What I've got to do, you can't be any part of. Ilsa, I'm no good at being noble, but it doesn't take much to see that the problems of three little people don't amount to a hill of beans in this crazy world. Someday you'll understand that. Now, now... Here's looking at you kid.

Trivia: Conrad Veidt, who played Maj. Strasser, was well known in the theatrical community in Germany for his hatred of the Nazis, and in fact was forced to hurriedly escape the country when he found out that the SS had sent a death squad after him because of his anti-Nazi activities.

Question: Why did Ilsa jilt Rick in Paris when she was in love with him?