I'm sorry you have lost your 'best friend'. I don't know if she died suddenly, but often a big dog will take a turn for the worse and go downhill pretty fast. If she was a small dog, 13 is not that old.
In any event, my heart goes out to you. Open your heart to the pain as you did to the LOVE. The Love will remain after the pain has burned away with time.
If I only knew that you were in pain I would have tried everything to ease that If I only knew that eight years is all I have I would have told you how