You sound confused and unsure of what to do. I think the diversity of opinions in this thread isn't helping. I'm going to take a different tack and try to help you get more information about this. Essentially, there are two places where you can get an answer to your dilemma, inside yourself and outside yourself.
You recongize that inside yourself, you are having difficulty dealing with this, however there are other ways to try. Perhaps consulting your intuition (there was a pavlina podcast about it), or perhaps reframing the question. Ask yourself how other people would solve this. Or how this problem will look from different perspectives in time and space, such as a year from now, and so on. There was a blog post about this, too, somewhere.
Outside yourself, you can ask for other people such as you did here. Another way is to find someone or some people who have experience with relationships to find the answer. A counseller or something.
Yet another way is to hunt around for books on this subject. I think Pavlina once recommended Too Good to Leave, Too Bad to Stay. I haven't read that book, so I dunno if it really would be applicable to you, but I'm sure others can also offer book recommendations. A few more books here:
http://www.stevepavlina.com/personal...ment-books.htm
The bottom line is this. This is a tough choice, and none of the options seem good to you. Many wonderful people have given their opinion on this issue in this thread, but the final decision is yours. Stay or leave. Let your imagination go for a minute and pretend what you think life would be like without her, or pretend-imagine what it'd be like a year form now if you stuck together. Try to get different perspectives on this.
I hope something here helps.