Sounds like your Ex does have some experience with mental illness. And regarding your fantasies, sometimes we have them to protect ourselves. Maybe you don't really want it to happen but maybe you have a deep fear that it could definitely happen with your ex. You are protecting your mind from any surprises by expecting the worst. It's a defense mechanism and a form of control. The smoking is a control issue too. If you wish to be in charge of your life and feelings then choose to control other things in your life. It's your choice!