I have had a crush on my sister for decades.

Brother, as a brother, you should put your mind right. You can't be with her. You are brother and sister, you can't be husband and wife.

There can only be affection between you, not love. Judging from your description, you have become a little obsessed and even fanatical. Has seriously affected your normal life. You can't go on like this. You're a little possessed now. Sooner or later, it will ruin your life.

I suggest you go to a psychologist, talk to the doctor about your thoughts and ask him to help you resolve your sadness and enlighten you.