You know the phrase ``the truth, the whole truth, and nothing but the truth''? Well, in this case I would suggest telling the truth and nothing but the truth, but I think telling the whole truth is probably a bad idea. Don't lie to her. You'd feel like a louse, and you'd be right. You don't have to tell her everything, though. You could even tell her straight out that the subject of past sexual experiences, hers or yours, makes you uncomfortable and you would prefer to drop it.