Why Am I In Love with an Imaginary Girl?

Every time I listen to an love song I think about this girl. Heck, not a day goes by that I don't think about her. She's has always helped me when I was feeling down. Then she became a dark signer and I had to duel her. When I was dueling her I realized that I loved her so much. I won the duel and before she disappeared, she called me her hero and we kissed each other. But I still don't understand how I could fall head over heels for her. I never thought that I could love another human being so much. So please, tell me what I should do.