It all comes down to your mind set and how you see the break up. A lot of guys will panic, beg, act depressed, act cold, or get angry. None of these things will work and will make you look like a weak man as well as cause you a lot of suffering. Don't self pity yourself or have thoughts like " how could she do this to me!" They won't help.
If you truly loved this girl you have to be cool with letting her go. Go NC under the mindset that your cool with the break up and your letting her live her life. If she contacts you talk to her like shes an old friend and be polite. This is a time for you to get your shit together. Break ups are amazing at motivating you to become a much stronger and better person. focus on your career, your health, etc...
A lot of the time the break up happens because the girl needs to learn a lesson or two and make some mistakes. You have to be cool with this and realize that and let her make those mistakes so that she can see just how great you two really were. It may take months, it may take years, but you have to be alright with it. It's how we learn.
During this time apart you will want to improve yourself as much as possible so that if she does come back after the mistakes, she has an amazing man to come back to. And if she doesnt come back you will definately meet someone else within that time frame.
That's the beauty of it as that there is no answer! You don't know what is going to happen in the future. She might come back or she might not, there's no answer! Drill that in your head! There is no answer for your dilemna! Only time will tell so use time as your ally in improving yourself for the best!