I have fallen in love with a girl please help me?

Hi there. So there's a girl in my bus and I have fallen in love with her. I asked her to be my girlfriend but she said no. I asked her like last year September. From that that day onward she is not going out of my mind. I like her a lot. And I can't get another girl becoz I want to stay single. But she is always I'm my mind. I am not able to forget her. Please help me. What should I do?