Here is the problem. Unless and until smoking becomes illegal, it is not the responsibility of your employer to ensure you absolutely stop coughing. It is the same with HVAC issues, wherein people have allergies or reactions to air conditioning or dust in the ducts. If the company attempted to rectify the situation, the other employee's tobacco smoke you smell on his or her clothing or person is not something that the employer can force the employee to change if it is not bothersome to others. Certainly the employer tried to rectify the situation and perhaps to be in your position, moving you farther away from the other would be disruptive to the efficient working environment. The other person doesn't have to be moved and if the company attempted to do so, then that person could sue for discrimination or retaliation. So your best bet is to see if you qualify for unemployment or disability.