You know what’s more hurtful than a breakup? A breakup that you didn’t see coming! This is something that happens often and we perceive as if everything is going great and your girlfriend just decided to end it abruptly, it could be that you might be the one ignoring signs or she just genuinely decided instantly, either way it just hurts really bad especially if you were giving it all and still want her back, if that is the case and she is gone from your life you can still do a couple of things to try and win her back and everything is not lost, if your girlfriend let you go and it is now over then it is even more difficult to get things back because you might not be aware of the reasons why it came to an end and many a times we don’t get that closure from that other person.
If your girlfriend has decided to end it and she’s out of the relationship without even discussing the reasons then there is little that you can do, in this situation you should talk to her closest friends, it is possible that she might have talked about it with them and you might get an indication from there, when you talk to her friends make sure that you only talk about the good side of things, don’t use foul language and never mention her shortcomings because that will only add fuel to fire, rather you should express how you feel about her and how you would love to have her back.
The most important factor which will help mend what’s broken is your maturity to take your responsibility and accept your mistakes that lead to the breakup and if you show willingness to put that right it will make things easier for both of you.