I'm sorry you are going through this. Yes it is gut wrenching. Right now it probably feels like you "lost the love of your life". If she left you, then she really wasn't the love of your life. It works both ways.
Take one day at a time. Enjoy your life. Don't do anything stupid like rushing into another relationship. Be strong if you are entertaining thoughts of getting her back. She'll respect you more than if you whine and beg. Get on with your life and try to find happiness. Eventually you will. It probably won't be easy, but nothing worthwhile ever is. You can either choose to be happy or drown yourself in self pity.
Good luck and get a dog!