How to get out of this mess?

I have been in a relationship with a co-worker for just a few months. We got involved a couple of months after he started. I got to know him, enjoyed his company and attention But before long, I had to face the fact that, for many reasons, that this was never going to work out-after I started to get attached. Yesterday, he quit the job. I see it as a perfect opportunity to cut all ties with him, but for these stupid feelings. Why is it so damn hard to let go of something you know is just a lost cause? Not long ago, I told him, "You bring out my inner crazy." His answer? "That's a good thing!"

I just found out he got re-engaged to his girlfriend. I was a rebound thing.