I'm so sorry about all of that. It's difficult to get over a serious relationship. Wondering where you went wrong is even more difficult, I feel terrible for you.

Personally, I believe that people don't need to feel regret as long as they find a way to get something out of their negitive experience. Nothing has to be for naught. In this case, you can make mental notes of what to do and not do in the future [whether you get back with her or find someone better]. Then maybe you can learn more about yourself through your actions/reactions....Including the actions/reactions to the break up itself. Think of this as a learning experience. But also understand why it's difficult to sustain a serious relationship at a young age, or with people who are youthful minded. This is life, take the oppertunity to learn from it. If you have an experience, positive or negitive, and you don't learn from it, then it was a wasted moment...You might as well try and get as much as you can out of it, especially if it's a negitive expereince. Why let it all be negitive? Try to block out the emotions and really think about the entire relationship...The parts you both played, where she was wrong, where you were wrong, what you both could have done better, what may have predispositioned the relationship to failure, etc. Don't be afraid to question yourself, and don't be afraid to question her. Logical understanding, for me at least, tends to help me find acceptance. I hope it does for you too.