So you've lost her. What now? Are you just going to sit and sulk there all day and wish she'd go up to you to tell you she wants you back? Well you could actually do that. Or you could smarten up and get her back. Yes, it is possible. In fact, every single day, lots of couples get back together. Even after years of being apart. All you have to do is remember the following things and you'll get her back in no time. Unless you did something really awful to her, that is. Otherwise, if the break up was just because of some petty quarrel or a little misunderstanding, these things should work.
First thing you need to do is give her space. You've just broken up and whether it was her fault or yours, it's mandatory for you to give her time and space alone. This is for her to think about and ponder on things that really matter such as why the break up pushed through, what caused it and the most important thing of all, if she wants to get back with you. Decisions like these cannot be rushed so don't pressure her into making one right away. While you're at it, utilize this time to think about these things, too.
The next thing you have to do on your way to get her back is to accept the current state of your relationship and think about things you can do to get it back to how you want it to be. Now, this is entirely up to you. No one else can decide what you have to do or need to do to get it back to how it used to be. After all, YOU were in the relationship with her, not other people. You know better than everyone else why you broke up. You may, however, ask for opinions and advices from friends and family.
If the break up happened because of something that you said or did, apologize. Tell her you didn't mean it and assure her that it will not happen again. Now when you tell her it won't happen again, show her you are sincere and prove to her that you meant what you said.
Get back in touch with her. If you've lost touch since the break up, you have to get back in touch with her at some point. If you don't do this, she might think you are not interested in picking up where you both left. Even if the break up was her fault, remember that you are the man and it is your responsibility to carry the relationship. When you get back in touch with her though, avoid making her feel obliged to talk to you or reply to your text messages and emails. If she doesn't pick up or reply, it might mean she needs more time to think things through. Don't worry, she will eventually talk to you again and that would be the perfect time for both of you to talk about things. An email or an SMS at least once a week will remind her that you still care but sending tons of SMS and emails and ringing her once every hour everyday might annoy her.
Lastly, if and when you've come to talking with her again, let her know why and how much you want her back. Be careful not to overdo it, though. It just might turn her off completely. Instead, reminisce with her old memories that testify how much you love each other. This would make her think about those happy times and make her realize how much she wants those memories redone.