I've been working with this girl for the past 9 months. She's highly attractive and a lot of guys are into her. For some reason, she's very attracted to me (I have no idea why) and has made it quite obvious. I for personal reasons have not reciprocated (occasional flirting aside) and have even let her know that we should stop talking to each other as its negatively impacting our work. Despite this, she continues to carry hope that we will be together one day and is always looking for me to escalate. Many girls I've come across in the past get permanently put off by the smallest thing e. g. they saw you talking to another girl. This girl however never seems to lose hope and is very persistent. I don't think she has any psychological issues and seems like a regular girl. My best friend also is in a very similar situation with a similarly pretty and persistent girl. My question is, why is it when these girls have so much choice, they hold out for just one guy and why do they never lose hope/give up?