@ehBeth,
I do not agree with you, the first thing i did was specify that i considered the information provided by my Bro, the OP, as not sufficient. And then proceed to state my opinion with what i got. Like two friends meeting at a bar doing small talk.
The rest of the posts had enlightened more information regarding this asset that had change of course the story.
So, Bro heres what i got to say (specifying that i continue in my bar-style way so picture you and me taking a beer on the counter listening whatever music you like):
You had a mistake that is completely natural, i had my own in the same way the first times i tried to start talking to girls. You are young and eager to react thats notting to be ashemed. Girls checking you out will be common. But this is a game of love that we can´t easily win so any moment to gather experience is necesary.
She had a BF so what? Forget that chick and move on. The future has the gift of the present but the past provides us with the experience. We must understand that women are complicated and misterious and must of the time we can barely know what they where really thinking.
So the best way to met girsl is the next: be natural, be outstanding in some way, and you must be on a place of exposure.
Be natural: do thinks you like, act as you please, and be yourself. Women had the role of choosing us not the other way. Acting in a holow way just attracts hollow people. But a stable personality attracts stable personalities.
Be outstanding in some way: like being courteous, or doing something really well done, or learning something not common. You define better your personality makes you different and is more likely to find a girl with your affinity
And of course be on a place of exposure: this is very important, if you like metal or something similar go to appropiate venues. I´ve known many gils trying to meet a good man going to discos and raves, and only finding one night stand jerks. The same happens to men. So go to places where you feel confortable where other people with your affinity meet and just talk about what you like. It easier to meet some good girl this way.
But the must important advice i can give you is the next:
Do not make finding a girl or a significant other as your goal for happiness. Look in your inside see what makes you happy and work over it, and the ideal girl will come. Looking for a SO is more like finding your number one fan, and you favourite performer at the same time. I can assure you the more you go looking for girls the more it seems like using repelent. The moment you start caring for your dreams you became more interesant to the other sex.