It is very sad, but the simple truth is that women usually move on emotionally long before they actually make the break. You may have already missed your opportunity to repair this. Give her the space she needs. Trying to hang on when she has lost the motivation to stay is pointless, and frankly, it might alienate her further.

FYI - If you have kids, my advice would be different.

PS - you really ought to give some thought to what REALLY happened. I don't believe for a minute that she was crazy about you one day, and done with you the next. These things take time to evolve.