Well first ask yourself, does she look happy now or not? If she is, just forget it and try to move on. It'll be hard but don't crush her happiness, your already an ex and that'll give her more reason to not take you back. Just be friends with her and tell her you'll always be there when she needs it. You'll regain her trust and she might be a friend which is better than nothing. Just because a relationship didn't work out doesn't mean you can't get a good friend out of it.
it will take time if she broke up with you then try to find someone who likes you for who you are if you broke up with her than you may want to take time to think about if you are ready for a relationship and what you are looking for in a girlfriend and then try again with some new stratigies
From experience, I know that it never works out the same or any better when u date someone more than once. It usually doesn't last as long and it's a little awkward. And plus, if u guys broke up, there had to have been a reason and that might come up again and it would just be worse the second time around. Sorry but my advise, just move on and try to find someone else. There's always someone else out there!