My brother's boyfriend has lived with us for several years. We live in a rural area on a farm. Which is awesome because I have asthma. Being out of the city helps me a lot. 

But boyfriend smokes. And he smokes a lot. And he will go stand right outside the back door and smoke. I have really sensitive lungs, and from anywhere on our property I get an asthma attack if he's smoking unless I'm inside. I have repeatedly asked my mom to mention to him that I have asthma and he needs to stop smoking because I can't breathe when he does it, and it's not like staying inside forever is exactly feasible. Like it's gotten to a point where I dread going outside because I don't know whether or not he's been smoking, so I don't know if I'll be able to breathe or not. 

Some more background info is that the boyfriend has never even offered to pay rent, moved in without asking my parents, and eats a ton of our food. Not a pleasant person to have in your home. 

Am I overreacting? Or am I justified for being angry about this?