You have two ways that you can go about letting go.
- The first is to accept the pain. Embrace your suffering. Admit that it hurts you like nothing else. Grieve for your loss.
- The next step would come easily after your acceptance. You then overcome it and because of your experience you become a new and different person. You are now stronger. I don't know if you are familiar about the saying: "Whatever doesn’t kill you only makes you stronger."
Letting go of someone you love is not going to end your world. You will have more good things that will come. Do not contemplate about the bad memories. Think of the good ones. Let it nourish and heal your heart.
Be thankful of the good memories that you've had and believe there will be more great things ahead of you. Giving yourself some positive focus and good goals to achieve will help you heal. Consume yourself in doing what is good for you.
You have to be able to move on. Winning this is learning that there is life after this relationship and finding that life. If you build a new foundation from the ruins of this relationship that has ended, chances are that you will be able to move on gracefully.
Find more answers to your questions. There is a book called The Magic of Making Up which talks about ways of getting you lover back if you think that the relationship is worth fighting for. And you can also find good advice on how to accept it if you there's really no hope for a reconciliation.