Oh , I am sorry you were hurt.
Unfortunately the reason you get (if you get one at all) doesn't always help, or isn't what you want to hear, but it still may be a valid reason.
You said
I had no idea anything was wrong! And the only explination she gave was "Your just not the right one," or "I just dont feel the same way anymore,"...
That may very well be her only explanation, peoples feelings change, maybe she really liked you but as time went on realized that it wasn't right for her. Things don't always end with a huge fight sometimes you just realize that you are going in different directions or your values are too different etc.
It of course is impossible to know what she was thinking, In my opinion you need to accept what she said and move on, and i know that's no what you want to hear but no one here as you said can tell you why she left because we don't know either of you.
I can also tell you you probably are not alone in
But i have no idea about women. I can relate to guys, but Im always one step behind with women.
The best thing I can say is listen, that's the biggest thing I hear my friends complain about, but that's just one small circle of people . But listening is key in any communication.
