First, read this thread: http://www.puaforums.com/become-pick...o-i-start.html
You are suffering from classical "Nice Guy" syndrome. In a perfect world, you would see a girl, walk up to her, say, "hi", and then doing something nice if you were interested, but that isn't how it works in the real world.
Put yourself in her shoes. She barely knows you, she knows that many guys are creepy, or worse. You seem like a nice guy, and she probably was even a little bit interested in you, since she told you she was single. All of the sudden, you went from guy, who seems nice, to "Here's a rose to express my undying love". At the best, she figures you are some needy leech, because obviously, you don't know her well enough to truly love her. So she immediately freaks out and ejects.
The previous paragraph is full of all kinds of logic leaps, but that is how your average women thinks. She has to, because the world has taught her that men just want to get into her pants, or they want to sap her emotionally. That is why you have to completely circumvent her defenses, and why you have to be an "alpha male".
If you really want to learn how to meet women, even if you are looking for the "one true love", you should read the books mentioned in the above link.