Why are you terrified of being alone? Do you think you won't ever meet someone this nice again, did you think that before her?

From the way you've spoken about her, it's obvious you don't believe you're a good fit. It's not enough for the girl just to be 'nice' - you've got to have some real, in-tune spark to maintain a full relationship.

You're not happy here, I would second what Dale said - make it quick. I think though that in actually writing that post you've already made your decision, you just wanted second opinion.