Allow yourself to be sad. Be sad, full-on, for a weak or two. Let it happen. Cry. Maybe play some games or something to kill time, but be sad. But also give a deadline when you have to stop. If you feel OK, make it a week, if it's tougher make it two or a month.
Then, when the deadline comes, add things back to your life. Hang out with friends. Do some things that maybe were tough to do when you were with her.
At this stage start to check out other girls. Not sleep with them, as that will make it worse. If you were really into your GF, no one will live up to her for a little while, so screwing whores will only make you feel pathetic. But do look at hot girls. There are so many in the world. Go to a mall, surf online...I don't find porn good, but check out Chive.com or other sites with lots of pretty, normal girls.
Then, when you're ready, go out and have fun and meet new girls and enjoy the chase.
I would only mix in alcohol after at least stage one. Alcohol is a depresant, so adding it to sadness will make you feel like garbage. Only drink when you're ready to be excited about meeting someone new and all the potential hot tail in the world.
