I skimmed, sorry. Paragraph breaks are your friend.
As for why your girlfriend left, and her reasons, those are her reasons, whatever they are. It's not for you to judge her reasons, even if you think they're stupid.
And you don't need to know if she was talking to someone else (what, the people you date aren't allowed to have conversations without your permission?) before the breakup. That way lies madness.
You're broken up. The cause doesn't matter. The reason doesn't matter.
What matters is for you to take care of yourself right now. Get therapy if you can, because breakups can cause a form of mourning behavior.
And if you can't, at the very least do constructive things for yourself, like watch a funny movie or go for a run or call a friend.
Dwelling on this breakup isn't going to make you feel any better, and it probably won't get her back, anyway.