She Lied She Is A Virgin, Should I Forgive Or Dump Her?

UNEDITED:

I have been dating a girl for one year two months now and I have always believed that sex is something that should be experienced only in marriage, and I still believe this.

But as our relationship grew, we became closer and closer to each other, and we both fell in love with each other, I honestly thought I had found the girl I. was going to marry.
However, as time passed, we became more and more physical with each other, and September of this year, we had sex.

Prior to having sex, I had asked her multiple times throughout our relationship if she had ever had sex, and every single time she would say that she had not, and that she was a virgin.
But about a week after we had sex, I asked her again, she got real quiet and said that she had to tell me something.
She went on to tell me that when she was 16 she had sex with her boyfriend of five months. She said that they broke up shortly thereafter, and that they only did it once, and that she just laid there, and that she just turned over on her side and cried afterwards because of how bad she felt about what she had done.
She said that for a year after, she struggled to get over it, and that she had considered herself a virgin when we had sex.

This completely broke my heart, I can't accurately describe how I feel, but it's a feeling of betrayal, anger, jealousy and just utter disappointment.
For sometime now, I have been struggling with my emotions over this, and I guess what I came here to ask is, should I just break up with her, or try to work through this? I don't know if I can trust anything she says..