it is no use to do this. Once a girl decides to leave you. She only feels troubled by all the things you do, rather than is touched by your change. It's most likely that she feels your change is temporary and not sincere. And what your ancle said is right. To build up a new relationship is much easier than maintain a old one. At the beginning of new relationship, both sides feel they match exactly. Only when time passed a lot, they can feel the other's shortcomings.

And more important, I don't think it's wholy your fault which causes the break up of the relationship. You seems looking for your problems all the time and keeping feeling regretful for that. Doing this only increase your guilt and pains. Any relationship is tied by both. And she is also responsible for it.

Imagine you were in the future of five year later. When you recall this, it may not be so painful and so important as you feel at present. You can still live very well, having a good job, owning a happy family or even having kids. These are possible! They are happening around us every day. Everyone has his pain and has to accept it, face it, and overcome it.

All I what to say is that you are very young and your personality is forming, unstable and unmature. Specially at present, you cannot judge correctly or reasonably on your thoughts and behavior.

There are many unpredictable things or pains happening in the future. You should learn to endure the painful feeling, and live with it well, and overcome it, then you mature a lot and be stronger. Just relax and focus on the things that you should prepare for your future, maybe that's the best way to win your girlfriend back.