just kidding, that was a little harsh.

Ok, here's my opinion.

She seems like a flirt, and constantly needs to know that she is wanted. The problem is that you may not fulfill that need right now? I mean, this happened twice with 2 different guys right? Like you said, she didnt want you until you didnt want her. Im sensing a little irony here. You found out and she is scared that (once again) you dont want her.

If you really love this girl, I think you have to let her go for a little. If not, this kind of stuff may keep on happening. Nobody deserves to get cheated on. I dont think forgiving her for something that she didnt even tell you about is the way to go right now.

Oh and once that trust is gone, the relationship gets sooo much harder.