Need girl advice on how to tell sister how i realy feel about her.?

I know this is not what you're looking for, but I believe you should see a psychiatrist to help you find the root of these feelings. I don't think you will ever be able to have a real relationship with your sister, and I think you should get some help to overcome these feelings so you can move on with your life and find a girl that you can actually have a relationship with.