Then after a while, try to be friends. That will be a foundation for anything that may come after. It might, but it also might not. But treating this as an adult is the best option you have of getting her back, because you are both adults. Trying to win her back immediately is showing that you don't fully understand her situation. You are being guided by your emotions which are not sufficient anymore. You need to work with your mind and do something that your heart might be telling you is wrong, and that is to maybe have one final talk with her to try to understand (preface this by saying that you are not going to plead for her to come back, you just want to better understand and know how to improve on yourself, this will in turn make you seem more mature and she might be more open to being a close friend after this, because a long relationship is a terrible thing to throw away completely), and then let her go.
Best of luck.