I have recently been meeting and talking to a lot of girls. I'm in a new city so I have a lot of opportunities to meet new people and there are definitely a few that I am very interested in, however I have had a slew of girls who appear interested at first and then seem like they lose interest. How do you recognize that an opportunity has passed you up or that the window of attraction has closed? Is there generally a set time limit or are there signals to recognize this?