This is a slightly long post. You've been warned.
Okay so straight to the point, I'm in my mid 20's and same age as her, and I've known her as a friend (casually, not good friend) for about 4 years now, and while I find her physically attractive, she was in a fairly long term relationship with someone and when we hang out with my good friend (through which I know her) and his friends, I respected the relationship and never at any time felt any attraction to her (also because I had my own fair share of relationships at the time).
Fast forward to about 4 months ago where we are both single now, and due to the locations at which we both work, it was sometimes convenient for us to meet (for lunch), which in the past was far and few between. Suddenly she starts asking me to meet her on a daily basis for these lunches, which I was more than happy to oblige. but I noticed that as these daily lunches went on, our conversation topics began get more intimate and deeper so to speak to the point where shes often put me in a situation where I am uncomfortable with answering some of the questions she asks me and forced me to lie. At that point in time I was still in the impression that she was in a relationship until one day during one of these lunches she drops the "we broke up 6 months ago but please dont tell any of our common friends about it because i trust you" on me. I wasnt surprised that they broke up but I found her telling me this and asking me to hide it from our common friends difficult to decipher.
In any case, as time went on she has started to become far more close, and we hung out more beyond the normal lunch breaks, and I would say that some of the things she has said to me has well and truly breached what I consider normal guy-girl friends behavior, not in a flirty way but emotional stuff that you should never have to say between friends ("i was really upset when you ignored my email" etc). Needless to say, that's when I started to develop feelings for her, which being a first time in this situation was something I did not foresee or could control. So I probed a bit without telling her how I felt and got back the whole "my mind is in a mess, I dont want to be in a relationship right now, i need time to be alone" crap, which made me realize that: 1. I am most likely in the friend zone with this girl and 2. Shes most likely unconsciously "used" me as an emotional band-aid after the long term relationship breakup.
So to wrap this all up, of course the best situation is that we become more than friends, because I realize that we share a lot of things in common and she is 'my type'. However, shes not some bitchy or slutty girl thats been around, but rather a truly decent person that has desires to settle down and I would hate for her to be hurt in any way (and I noticed that she is a little sensitive emotionally than all the girls I know). That said, I'm not content with just letting this go by silently because its far too painful for me to keep these feelings like this, so I feel that it is necessary to tell her in some way my side of this whole situation (including the part where I like her as more than a friend), mostly due to actually wanting to know what was going on in her head and of course in the off chance that she actually may see me as more than friends too.
Whats the best way of expressing my feelings for her and relative frustration in the way shes behaved towards me?