Sounds like you had a better night than me. Some bitch stamped on my foot, poured her drink on me and then pulled my hair. All because I wouldn't dance with her. I hate drunken teen girls.
Oh yeah Dave, I'm sure he feels better now! He's trying to just get one girl to dance WITH him and here you are beating them off with a stick.
Back on topic Psychology - what'd you do wrong? You didn't wait long enough! Just because the guy says the relationship with her won't work doesn't you march right over there and try to pick her up. She doesn't know it's over yet. Hell, HE doesn't even know it's over yet, he's just sure it won't work. Your move is next week, not 1 minute later.
You're doing fine dude but remember - Drunk girls will play games, even more games than they already play when they're sober, so you HAVE to be prepared for a whole lot of chicanry, evil ruses, and ulterior motives. The female of the species is a crafty query but, with enough experience and patience you will learn to rope them in. So much to the point that eventually you will laugh at how easy it is to pick them up, or so I've been told at least.
Point is, like everything else, practice makes perfect. The first few times some drunken girl flirts with you, you may not recognize that she's just having fun, watching you fawn over her, and stroking her own ego. But they don't always do that. There will always be some that are actually looking for a hookup, if not more. The only way to learn the difference is to experience it a few times. And believe me, it won't take you many times to learn the difference between some drunken floozy flirt and one that you may actually have a chance with.
Keep diggin', you'll get there.