Honestly, that question coming from that girl with that look fills me with overwhelming dread. It's a trap. No matter how you answer, she won't like it. Tell her the truth, she'll think you're lying. Tell her a lie to avoid an argument, she'll stalk you and find out you were lying, and she will hold it against you forever. She might not show it now, but this is how it always starts. With a smile, and what you thought was a harmless question.
I know she's often depicted as the crazy girlfriend, but it's usually so exaggerated that it's more funny than anything else. This... this is different. Too real.