Abcdx, I've got to agree with coco's mama on this one. I would forget about her and move on. It sounds to me that she had opportunity enough to start something with you if she wanted and she didn't - so I'd let it go. It sounds like you have been a great support to her and a great ear to bend - and you will make some woman very happy, trust me. But this particular woman I would let go - for basically the reasons coco's mama spelled out - she leans on you for emotional support and probably makes herself feel better in doing so - but does not let things progress futher. Intentionally or not, I think that qualifies as using you. Furthermore, girls who e-mail guys about all the fights they are having with their current long term boyfriend - red flag right there - Do you have any reason to think that type of behavior would change? Do you want YOUR girlfriend e-mailing other guys about your relationship. Yuck. Get out.
There are so many nice girls out there who would treat you better than that - but you won't find them if you have blinders on and just pine away for this one girl. To be honest, even if she ended up calling YOU and telling you she had all these feelings for you, I would STILL be nervous about getting involved with her... its her pattern of behavior that makes me very uncomfortable. Like I said, it might not be intentional, but it is not fair to you and that should be enough for you to walk away from it. Just take a break and get yourself doing what you like to do, and you will find better things. Good luck.