Tell them it's your boyfriend's but not to worry because you are dumping him for refusing to respect your quite reasonable requests to not stink up your stuff with his personal habit. Seriously, why are you with someone who ignores a simple request unless he actually owns the place and you will be homeless without him. I say owns because few rentals allow any kind of smoking inside and if you are on the lease you are going to be responsible for his smoke damage. Or just tell them the truth and let them feel how they feel. There comes a point in life where you just deal with the realities of life as they occur instead of wearing yourself out with useless what ifs. Good luck.