Is it normal i do this to a girl?

Ok so I am really attracted to this girl and I think I am becoming obsessed. I once sat beside her in class and attempted to stick my hand down her pants but she got up and moved to go get something. The next day I followed her to the changeroom and wanted to get a peek at her nude, but didn't because I knew it was wrong. I masturbate to all of her insta pics and I want to fuck her hard. She is short (my preference) with black and pink hair. What really arouses my is her ass and how small she is compared to me, meaning I would dominate her in bed. I know where she lives because she is also my friend and lives near me I have been to her house I want to get in her room when her parents aren't home and close the door and see if she wants to have some fun. I would only do it if she wants it. Her older brother thinks I'm a creep and wants me to stay away from her, but she says that I don't feel that way about her. But I do. Is he right? Is this normal?