Hi seddit. I'm relatively new here, i'm seeking some advice.

Tonight at the bar I spent about 2 hours chatting this girl up, eventually leading her to the dancefloor where it was getting heavy to say the least. Eventually it quites down and we go outside to chill and talk. On the stairs, some random guy who supposedly knows her (though I found out only met her at a different bar last week and thought he had hit it off with her) comes, drags her away, sits between me and her, and makes it very difficult for me to even talk to her.

She talks to him for a little bit, while i'm left wondering what to do, but eventually just decides to leave with a friend. At this point, she is not even interested in me anymore. I didnt even get a number.

I'm just bewildered. I'm new to this subreddit, and to picking up girls, and this has never happened before. What am I supposed to do in this situation? How do I prevent it or at least keep her interested?