I understand your pain jnallen. Here is what I am learning from a a similar experience:
1) It has nothing to do with you. I know (trust me) that this is hard to internalize, but its true. You're not perfect, but if you are willing to talk things out and she isn't then its a problem with her, not you. You are being reasonable, she isn't.
2) She probably isn't really THAT nice. I was thinking for the last 6 weeks that the chick that dumped me was nice. Then last night I thought: why is she nice? Because she was ****ing with me (intentionally or not)? Because she used me when she was feeling down and then left? Because she gave me some attention when I was lonely? See what I mean? Look at it more objectively and I think you'll see that she's probably not THAT nice. That's more a way of you justifying still being obsessed with her to yourself.
3) I could be wrong about this, but you probably don't miss HER. You miss what she represented to you. For me at least, it has nothing to do with the specific chick and a whole lot more to do with my own feeling of needing to be loved or accepted. I didn't know her long enough to have any legitimate feelings for her, but b/c I am so unstable right now emotionally I used her to feel better about myself.
4) There is no certainty in relationships. Pretty sure you're aware of this since you're divorced, but remember it. It's a hard paradox b/c the only way you can have a truly decent relationship is to put yourself out there, and you will almost inevitably get f*cked when you do that. But what are the consequences of not doing it?
5) Try to think about all the things you DO have. I am in grad school, financially (somewhat) secure, lived abroad for 4 years, have better guy friends than almost anyone I know, etc. So I don't have a GF. I want that eventually, but I am still really lucky not to be working in a f*cking factory with a wife that is insane or a drunk. You see my point.
Hang in there. Oh, Don't have sex with her or beat off while thinking about her. This is hard for me (the beating off), but it only serves to reinforce those feelings in my belief.
And if you feel really bad, consider going to talk to a counselor. Maybe it will help you to see why you are fixated on one person. It's usually a symptom of something else that is lacking in your life.
Hope that all might help more than the usual harshness that most guys here respond with. Life isn't as easy as "Just deal with it" or "get over it". Not in my experience anyway.
-Swigue