If you lie, i hope you have a good memory to avoid future slip ups. Women have a knack to remember what people say months and even years after.

If you don't lie, chances are that she can get angry. It is her right to get angry.

What about her leaving you? Frankly, i'd say its the best if she leaves you - Why? Because for someone who is immature at not accepting another person's past - better not to stay with them.

Everyone has one time or another made not so ideal choices. So yeah at one time, an individual was a little rash, out of control, slept around abit.

A girl who leaves a guy because he's poked around other fishing pond is immature and likewise
A guy who leaves a girl just because she's not a virgin due to some impulsive decision is also immature.

Grow up. Learn to accept people for who they are, both good and bad.