Love is a very good feeling, we are wish to have someone who we can love and get the love back in return, it's the only way to being satisfied with the relationship but obsession is so wrong in many ways because it's definitely going to drive you into doing so many things that are so wrong which you are not supposed to. Some the things which obsession might push you into doing are even against the law. Take for instance, you made mention about stalking the girl. To stalk someone is completely against the law and if the person reports you to the authorities, they would have you arrested. Yes, I understand that you truly love this particular girl in question but going through this process with obsessing over her is definitely going to make you lose her. Express your love for her in an honest manner and wait for her to love you back.