How can I end this relationship?

I know I need to leave my girlfriend for very good reasons. All my friends and family have told me I need to do it but the problem is that not only is she immature and spoilt, extremely prone to tantrums (she actually folds her arms and starts breathing heavily when she's mad) and revels in the pain of others she believes has done her the slightest wrong, never says sorry, never believes she does anything wrong, always talks as if she is always right, believes her advice is to be adhered to and I could go on.....so not only is she all of that but I sit right across a desk from her at work.

I'm not insanely career minded but I do think I can do well in my current job and I like the company and the people in my office/building quite alot. I have tried looking for another job but it's not materialising at the moment.

She is driving me insane, I mean literally beating my head against a wall insane, literally! I talk to myself about her openly in the street and I don't care who hears me. I have shouted at the top of my voice when I've been on my own and we've been arguing. Sometimes I can almost feel my blood pressure rising by the second.

I'm a naturally calm and decent person who is very laid back and I normally don't care much for what others think of me as long as I'm a good person in life. I hate drama prefer to avoid arguments but I will stand my ground. I am changing when I'm around her. I live in not quite fear of saying or doing the wrong thing but close to it as everything seems to upset her and arguments over the most minor of issues last for days. She has insecurity and confidence issues and needs to be with around or talking to someone constantly either in person or by text or she doesn't feel needed or wanted. Nothing I do is right in her eyes unless she told me to do it. I can't even book holiday at work without okaying it with her. We've talked about both of our issues and I acknowledge I am far from perfect! She doesn't accept that her issues exist mostly. Even her Dad said that she is spoilt and they have a great relationship. We had a massive argument just after Xmas that left me crying uncontrollably in a public space and I lost who I was for while.

I don't want to end up hating or resenting her even though I realise that this paints a rather demonic picture of her. She does have her good points and I would wish that we could someday be friends although I don't think she would be capable of this. So given that I would prefer not to leave my job how should I end this relationship or should I say "delationship" because it's deflating the life essence out of me!!!!..????