Break ups are, to put it mildly, a pain in the neck. The causes of splitting up vary, but whatever the cause, it is quite common for one person to want to get back together. Let's assume that you are reading this because you're a guy, and you have already tried to work things out. However, she brushed you off and now you're asking yourself, "how can I get my ex girlfriend back when she needs space?"
First, you need to accept the fact that she needs space. Emotions can get chaotic after a break up, and you both need some space so you can get things back under control. Perhaps you have already reached that point, but your ex girlfriend hasn't. On the other hand, maybe you haven't calmed down all that much and you are reacting too quickly. If this is the case, then the best thing to do is nothing. Just wait for a while and give yourself a chance to manage your feelings.
"Hold on," I can hear some of you asking, "what if she is only saying she needs space so she can get rid of me?" That's a fair question, and there may not be an easy answer. However, if you started trying to get back together the day after you broke up, then there's a good chance she is telling the truth. On the other hand, if you have seen her hanging out with a new guy, and it's been several weeks, then there's a possibility she's using the need for space as an excuse. It may not be easy, but do your best to use logic hen trying to determine if she's making excuses, or if she really needs the space.
If she is only making excuses, then you have nothing to lose; you may as well have a heart-to-heart talk now and see if there is any hope for saving your relationship. Most relationships can be saved, but if it just isn't meant to be, then it's best to know that as soon as possible so you can start to move on with your own life.
However, if she is not making excuses, and just needs some space for a while, then you should give it to her. The tricky part is figuring how much space and how long you should wait before trying again. You should know your ex girlfriend better than anybody else, so you will have to use your better judgment. It is even possible that she will be the one to contact you first, but only if you give her enough time and space to sort things out on her own.
There is another thing to consider when asking "how can I get my ex girlfriend back when she needs space" and that is that you don't want to appear too desperate. If you come on too strong she will feel smothered, and that will only work against you. So, play it smart and do things right.