I'm there right now as well. Been dating a friend, which was going somewhere only to blow up in my face. Admittedly, I made some mistakes (wasn't aggresive enough in hindsight, and it was doomed beforehand I guess as she wasn't as invested in it as I was). Well, last week she told me it would be best if we didn't see each other anymore in person, at least for a while, and I felt relieved and sort of better the first days. But now my life is like a living hell, and she's on my mind 24/7. Along with other crap that's happening in my life I feel like I'm sliding in a depression, so I've made some decisions that'll hopefully get my life back on track (moving out of here and get my own place, get more socially involved if time and money allows). But all that won't fix her being on my mind constantly. Only time can do that, so the only meaningfull advice to give is hang in there, and perhaps open your eyes to other opportunities (girls) out there. Rationally I know I'm being an ass for feeling so down over things not working out with this girl and that i should get out and live life and meet new people. I'm going to try and give it a shot. I think you should too.
On really romantic evenings of self, I go salsa dancing with my confusion...