How do you deal with someone who know too much about your secret?

Stop telling people your secrets.

Let them do what they will. If they know you're worried about it then they're almost sure to tell your secrets. This was a good lesson to keep your secrets to yourself. I wouldn't worry about them. They're going to do what they will. Don't even discuss it with them. Go your own way if you have friends that are not trustworthy. Never allow anyone to blackmail you. Just keep your secrets to yourself.