Getting your girlfriend back after she walked out on you requires a lot of patience and determination from you.
She was obviously so sick and tired about something in the relationship, that she couldn't take it anymore, and walked out on you.
This is where the problem lies, and what you need to fix to get her back again.
You need to be honest with yourself here.
What did she complain to you a lot about? There had to be things that you were doing that really irritated her, and when she complained about them, you ignored her because, to you, they where small, trivial things that didn't matter.
But they DID matter - to her they were so irritating that she couldn't handle it anymore, and got tired of asking you to stop doing those things, and in the end, walked out on you.
Whatever these things were, you need to make a real effort to stop doing them right away.
If you were in the habit of doing certain things that made her mad, start practising now, and get out of those habits - they're irritating to her! Getting your girlfriend back into your life again could very well depend on it.
Once you have given her enough time to get over her anger, make contact with her, and ask her to meet you somewhere.
If she agrees, make sure that you have a great bunch of flowers to take to her.
This will immediately soften her up a bit.
Then, tell her that you realize what it was that you were doing that was really annoying to her.
Also, tell her that you have stopped doing those things, because you now realize that they were making her unhappy.
Then, let her know just how much you love her and need her in your life, and tell her that you are missing having her around.
Her reaction will tell you whether you are getting your ex girlfriend back or not.
The chances are, you will get back together again, because, she will really appreciate the effort you have gone to in order to make her happy.