I love this thread. I've being reading it for the past week or so, and I finally caught up.
I want to share a little story of mine. It's not exactly what OP is asking, but bear with me.
I was studying English at an English school (I live in South America) and this girl, let's call her "L" worked there. She seemed very nice, always smiling everytime I saw her. One day she added me on Orkut. I talked with her a couple of times through MSN and decided to ask her out, and she said: "Sure, why not?". Shy as I am, I was pretty happy this was much easier than expected. We were going to get some ice cream or something. She described to me where she lived so I could take her on saturday.
Finally saturday night. I decided to go some minutes earlier so I could find her house, but the thing is, I didn't! Holy crap. This awesome girl wanted to go out with me and I couldn't find her house. I tried to call her, but she wasn't answering. I went to some houses there and asked "Does L live here?", but nope, no luck. Half an hour later I gave up, and I was devasted.
A couple of days latter I talked to her on the phone and apologized. She said it was no problem because she had a cold anyway.
I don't remember exactly what happend right after that. I think i tried to set another date but she said she was busy. Oh well, time to move on. We still talked from time to time.
Fast forward a couple of years latter and I decided to ask her out againg. I live in a small city, and we worked less than a mile from each other. I decided to walk around the street that she gets to go home after work to try to find her (a little creepy, I now realize that). I'm not sure how it happend, but I finally got another date, and this time I knew where she lived!
So we went on a date. The talk was very good. She always looked at me and smiled. Not much latter, she asked if we could call it a night. In the way to her home, she said that they were going to watch a movie or something in the next day, and that she would call me so I should go. I thought "awsome!", but... she never called.
I got very, very frustrated. I didn't now what the hell was going on. The date was good. We could talk a lot and not get bored (I'm an expert about realize when people are bored with me). I really thought she liked me. I tried to set another date latter on, but she said she was busy. And busy later on. And busy againg. So, time to move on again, I guess? I did that.
I remember that we used to send SMS messages, sometimes kind of flerty, but very, very light. I still remember that once she wrote something like: "If happiness comes like drops of rain, I wish you a rainstorm".
All this time I never see a picture of her with anyone on facebook or orkut. She also never changed her relationship status to "In a relationship".
Fast forward an year or so again, maybe two? I don't really know anymore. I saw her on the street and oh my god, she looked prettier than ever. It was near christmas. I thought what the hell, what do I have to loose?, and send her an SMS saying: "I don't know if you know, but I like you. I mean, I really, really like you". It was the first time that I was really direct about my fellings. She didn't answer. I send her a christmas message and that, she anwser. She also spoken to me on facebook, telling me that a friend of her wanted a kitten, and my cat had just given bith. Well, I sended her a couple more messages about my fellings after that, and againg, she didn't say anything. She responded my new years message, though, so I knew the problem was not that she wasn't seeing her messages or a broken phone or something.
It became pretty clear to me that she didn't want anything to do with me. So, somehow I thought it was a good idea to tell her everything, about how liked her for so long, about how I felt when I didn't made to her home on our first date, everything. It was huge. Like a big love email. She didn't said a thing!
So, me being stupid, I went full "pls respond" on her. Now I ashamed about how I dealt with it. Almost a month worth of "pls respond" latter she said: "Well, let's just be friends". I responded something like: "Oh, ok than

". Now I was sure that was really time to move on.
A month latter, her mother died from cancer. I knew her mother was sick, but I didn't know it was so serious, let alone it was a freaking cancer. Mind you, in my country we live with out parents until we get married, so she still lived with her mother, and they probably were very close. So, I was pressing her with meaningless stuff exactly at what probably was the most difficult time of her life. I fell so bad every single time I think about it.
As of now, I still send her a "Merry Christmas" message or something like that, but we never really talked anymore. I don't really think about her anymore, but up to this date I still think that she's the one that got away.
Edit: It feels good to finally tell this story to someone. I've never spoken to anyone about it.