This is going to sound very trite, but time does heal all wounds.
A friend of mine got dumped by his fiancee not too long ago. They had been dating for 3,4 years, something like that, had gotten engaged, and had even bought a house together. Then she dumped him, just like that.
He was pretty broken up for quite a while, but then he took up ballroom dancing to get out of the house and get active, and, wouldn't you know it, met an absolutely fantastic girl there who he hit it off with, and now is apparently happier than ever (at least, last time I talked to him).
It'll be really rough at first, but you'll get through it. And maybe even come out ahead in the end. Until you do, the advice everyone else is giving is good...do something to get your mind off her. Get out, exercise, spend time with people...your friends, not hers...engage in activity, try to pick up a new hobby...
And come here to vent whenever you need to.