Tell someone how you feel when they ask you to keep a secret for them, do not worry about this.
When someone asks you to keep a secret for them today, be honest about how you feel. You know how doing things like this affects you and you find these situations difficult and uncomfortable, so do not agree to protect someone elses secret if it unsettles you. Do not let this worry you, just tell them in a polite way that you cant do this this time.