I don’t know if you’ve gone mad. But I do think you should be in jail. What you did to your cousin is illegal in most parts of the world and for good reason. At 11, she was not able to give consent. You took advantage of her. It seems to me that what you are calling love is your attempt to justify what you did. At 15, she’s still too young to consent and may be so confused by what happened that she doesn’t know how to end contact with you entirely. The best she’s been able to do is not respond to your advances.
Get out of her life. Get yourself some treatment. If you really love her, admit what you did to her parents so they can get her the therapy she probably needs.