My condolences as well to Sebastian.
Rain Dog... Many here have already given you some golden perspective. Here's my two cents.
My marriage ended 3 years ago. Although I told myself at the time that I accepted it and was ready to move on, I'm only now truly starting to come around. And it's hard. In my case, it isn't easy because I still have contact with her... There's a kid involved. These things all make it a lot harder to just let go.
When she first left, I quickly entered into a deep depression... And I was drinking at least a six pack every night just to be able to fall asleep. It fucked with me at work to the point that my supervisor had to have a talk with me. The point being: I didn't do the smart thing and I let my depression get the better of me. The important thing to remember is that when you hurt yourself in this way, you're the only one that really gets hurt. Once you realize that, you see how pointless it is. You think you're lashing out at her by hurting yourself. Almost like you want her to see how broken you are because of her actions. But that's absolutely the worst thing you can do because it only makes you more pathetic. And she's moving on as she has a right to. So should you.
Of course you will miss her. And you will miss her, most likely, forever. Because people are different. So, even when you move on with someone new (which you will, eventually. Don't worry about that.), the ex will occasionally pop up... In dreams... In thoughts... She was an important part of your life for so long that you wouldn't be human if a residue didn't still remain. But, in time, you will hopefully be able to look on that as a fond memory, rather than a source of heartache. You loved, man. And the fact you did so honestly is a gift. The fact you can feel that is a gift. It's the cliché of 'it's better to have loved and lost..." but as lame as that sounds, it's actually true.
And as far as missing her is concerned, you will find in time that what you actually miss are the moments. You miss the relationship itself more than the person. You say it came as a shock. But if things ended so suddenly, it means they were probably headed downwind for some time... And, once you have some perspective, this will become clearer to you. Things couldn't have been great. If they were, things wouldn't be over.
In a situation like this, you may find that you want to blame yourself. It's kind of natural. "Why was she not happy?" "What did I do wrong?" "What more could I have done?" The answers to those questions are 'it doesn't matter' and 'nothing.' A relationship can only truly work when there is mutual contentment. If one of the parties is unsatisfied or unhappy, it won't work. But this dissatisfaction is not necessarily because of the other person. Sometimes it just is. Clearly she needed something else. That doesn't mean another person. It just means that the space the two of you were inhabiting was not what she wanted. And that's really nobody's fault.
Healing is a bitch on this sort of thing, man. My wife and I were only married for 4 years. But this is a woman who was a very important part of my life (as both a friend and a lover) for 15. And the end result is that it's a little bit like taking a carving knife to the slab of meat that is your life and lopping a huge chunk off and watching it slap onto the tile floor of your kitchen. It feels like shit, of course.
But remember that you are not alone. You do have friends and people who care for you. Reach out to them and they will be there to see you through this. It is in moments like this that you discover who your friends truly are. And the great value of these friendships. I eventually have found my way through this with the help of some dear people in my life. You will too.
I'm still there. It's an uphill battle... But I am definitely better now than I was in 2008. And I will get better still.
Also... 2008 is the year I became a really active poster and blogger around here. And I can assure you that is not a coincidence.... I actually owe Chud a small measure of my sanity. So all the advice that screams: FIND A HOBBY - FIND A DISTRACTION... Sound advice.
As far as the future? It's taken me this long to even consider the possibility of entering into a new relationship. Not the actual doing... The considering. But I guess that varies. One thing that is certain is that it won't be a real relationship until you are very much healing or totally healed. Anything before that will pretty much be brainless fucking.
But brainless fucking has its advantages as well. So don't be afraid to try some of that when the time comes.