Honey, I've been there a couple of times myself and it's the most awful feeling in the world but I promise you it will get better over time. i know you probably don't believe that now but, trust me, it will.
I think it probably all seems so much worse because your mates are away to uni and you've lost some of your support. Usually I go out with my pals if i've had a bad break up, get horrendously drunk and snog some random if i've had a really bad break up, but you're not only adjusting to life without your girlfriend but your mates too.
I always find keeping myself busy helps - do you have any other mates from school or work that you could kick about with, maybe organise a works night out or maybe take up a hobby or a sport? I know it's not always that easy to do but you'll find that getting out there and meeting new people will help you stop thinking about it so much and help you to move on. You have to be proactive and I know it can be hard sometimes to pick yourself up when you're feeling down and lonely but you'll be amazed how much better you'll feel.
Have you spoken to anyone about how you feel? Your mum or dad, family member or friend. Sometimes a great big hug from someone close reminds you that you're not on your own and sometimes saying it all out loud helps you get it all into perspective.
Let me know how you get on or if you want to chat about it some more xx