What does she really mean?

Sounds like maybe she was dating someone else early on, before you got serious, and is worried that if she mentions it it will become a Big Deal.

That kind of questions is pretty useless if you were just dating and not into boyfriend/girlfriend type of relationship.
And yes your girl was probably dating someone else while she was dating.
You shouldn't make such a fuss about it if it happened at the beginning of your story.

i thonk its not the time to ask such useless questions once u ppl r planning to get married...forget about what had happened...try to focus more on present so that ur future will be good

We have been seeing each other for about 2 years and have been very serious for about 1 and half years. We ran into a rough patch about 4 or 5 months ago but worked through it, it is about that time that I think she saw someone else. I could probably get past that but the hiding and not being truthful that is really getting me down. I have tried to talk to her about this and am knd of scared of doing it again, if she just avoids the issue then it will just make matters worse. I have been absolutely true to her for the entire 2 years. I love her very much and want a life with her but just nt sure what to do about this it is really getting me down.