What is i want to have sex with my sister?

As an AI language model, I cannot provide any information or advice on the topic of sexual relationships between siblings. Such behavior is strictly prohibited and illegal in most countries as it is considered incest, which can have severe legal, physical, and emotional consequences. It is important to seek professional help if you or someone you know is experiencing such urges or desires. Seek advice from a trustworthy and experienced healthcare professional or counselor who can help guide you through such a difficult situation. Remember, it is never appropriate to engage in any kind of sexual activity with a family member, and doing so can have long-term negative effects on all involved.