Delta, I understand your pain. But it could be worse - imagine the new guy WAS at work and you had to endure them making glances at each other all day!
You say you've "nexted" - but you're not over her. Sure, you actually HAD a relationship with her, that's a step above a oneitis. But you still have feelings here - you're not over her. Your reason may be a little more "valid" - but a bad oneitis still affects brain chemistry in a similar way, IMO.
The optimum solution in this situation (or a oneitis) is getting away from the chick and never seeing her again (or at least very rarely). It takes time away to "heal". But you can't because you have to see her every day. That's tough. However, there are other things you can do (and the progress will be slower, but it WILL work - you have to take it one day at a time).
Ignoring her (and/or effectively being rude) will only backfire on you (and guess what, it really doesn't help that much because she's there anyway). She will notice it, probably tell other people about it, and you'll just have the headache of other co-workers thinking your an ass. I don't advise it (even though it feels like you just have to or you'll go insane). Also, chicks can be complete underhanded b1tches if you offend them, so assume she would do something to fvck you over.
However, you can avoid initiating anything with her, if she talks to you, YOU HAVE to be polite (don't be abrupt/short - it will show). But don't prolong the convo - make answers that don't lead anywhere. And if there's any situation where you have a choice whether you will or won't be around her, take the latter.
If you can think through things you don't like about her and even actually get yourself a little p1ssed about things she did to you, that will help. Write them down and try to remember them often - you seem to have her a little on a pedestal right now. Does she even care about you? (You say not, so why would you care about her!) You probably remember the time when you were together and you liked that she cared about you - well now, you're going through this hell and she doesn't care! Try to "realise" you broke up for a reason, that reason is still there, and getting back with her wouldn't fix it.
If you get thoughts in your head of her, or her and her new guy, or anything to do with this issue, put them out immediately and start thinking of something else (don't even finish your thought trail on her). DEFINATELY do not visualise details of them together in your head from the stories you hear. The more you think of it, the more ingrained the feelings get and the longer they take to fade. Try this tactic - if you can do it, it works.
Of course, meeting other chicks will help. It's hard when you're in the mood you must be in, but it really would help a lot.
Don't jeopardise your finances/career by quitting unless you can go to a BETTER job. If you can do that and you want to, do it. Otherwise, stick it out - it will be OK in the end. Take it one day at a time.
The final thing I want to say is - NOTHING ever stays the same. Something will change - she may leave, she may break up with this guy, you may get a better job, and certainly you can be sure your feelings will fade.
. It seemed like life had dangled happyness just out of reach.. and then as I stumbled to grab it, something decided to shove a red-hot stick of FVCK-YOU up my otherwise virgin a$$hole. I remember one particular incident in a cinema where, metaphorically speaking of course, I wanted to FVCKIN DIE. 
