It has been said that when it comes to some parts of life, you can never really get out. While that might be true if you are involved in the mob or something, there are no relationships which exist between consenting adults in which either party can not eject at any moment when it suits them. Of course, there is a lot of emotional baggage that is going to have to be dealt with, if you really do decide to cut and run from your smoking love. Undoubtedly, there is also going to be a fight before you get out of the situation, as well.
Getting out of a situation in which your partner is harming themselves can often become somewhat of a codependent scenario. On the one hand, they can always come back with the question of whether you love them or not. And no matter what you answer, they are inevitably going to think that you are leaving because you do not love them. If you explain that you want to remember them as vibrant and healthy, and not as the rapidly dying cripple that they are going to make themselves, they will not understand what you are talking about. Smokers are sick people, even before lung cancer and COPD manifest themselves in a noticeable sense.
And they will fight you over your decision. In some cases, you may end up having to physically fight your former love, just to get out of there. In some cases, they may do such disrespectful things as blowing smoke in your face. While the temptation will be there to hurt them as much as they are hurting you, remember that it is their illness speaking, and not the amazing person that you remember. There is no sense remembering them as a twisted mass of illness and disease, when you know that they could have been more.