Letting go of someone...
I have to speak from my newly mended heart on this one.
To jump into another relationship right away is like putting a band-aid on a gaping wound. The hurt is only going to get infected and incarnate itself into your next relationship if you don't let it heal before hand.
Time...though that is a vicious cliche, it is a cliche for a reason.
Try focusing, not on the pain of severing, but rather on the lessons to be learned and, when the wound has healed enough, the great things that came from your temporary union that will add to the experienced, amazing person you are.
Support from friends and family is vital. Retain your individuality and don't let yourself lose your identity into the person you are separating from.
Letting go of something...
All I can say here is that "things" do not define you. Though an object of sentiment or even a house or business you've put so much work and memeories into may seem to be an extention of yourself, don't let yourself be fooled. At the end of the day, what's inside of you is what will always be there and it's what will make all the difference in the future.
And they all lived happily ever after...the end.