I give myself one day of self-pity. Do whatever it is you need to ... depressing movie, gut-wrenching breakup music, alcohol ... chocolate ... EDIT: If alcohol is involved, sweet god, GIVE YOUR CELL PHONE TO A FRIEND. Lol. Drunk call/texting ... not ok.
And the next day, I pick myself up (possibly hungover) and move on.
I can't vouch for everyone, but all I can say is that I've been through this enough times to know that the pain will pass. Slowly, you won't think about him 400 times during the day. But give yourself time, be patient, and make sure to surround yourself with some great friends who will help distract you, who will put up with you talking about how much you miss him for the 10,000th time ... and then will give you a nice little bitch-slap of reality to bring you to your senses.