Life turns on a dime - it's all a statistical odds game - no matter what it is - a girl you'd like to date, the size of your bank account, where you'd like to travel, the way to make any of these goals actually happen is to increase the odds they will happen: and that means being active - not passive - do something (think it through first). Not much ever happens to bystanders in life.
You should not give up because the guy could be interested in you and not her. The best thing is to do is talk to him and find out what he thinks about that. If he likes her, then maybe you can give up.