All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is no doubt that smoking has extremely harmful effects on the smoker as well as on the people who are present with him when he smokes. This is what doctors call "passive smoking" and it can be even more harmful. Since smoking is filthy and causes harm, the scholars have issued Fataawa that smoking is impermissible. Please refer to Fatwa 127405.
The best that we advise you to do is to supplicate Allaah for this man to correct and guide him, as supplication is one of the most effective means by which a Muslim achieves what he desires. Hopefully, your husband will repent and completely stop smoking and the problem would be solved. So, supplicating for him should not be overlooked.
We also recommend that you continue advising him and not despair of the mercy of Allaah. Allaah said on the tongue of Ibraaheem (Abraham), may Allaah exalt his mention, (what means): {He said, "And who despairs of the mercy of his Lord except for those astray?"} [Quran 15:56]
If he repents and turns to Allaah, then praise be to Allaah. Otherwise, you have the right to ask for divorce due to the harm. For information on the valid reasons for seeking divorce, please refer to Fatwa 131953.
On the other hand, you should endeavor to convince those in charge of the Islamic Centers in your area to keep you out of harm's way either by divorce or Khul‘, and remind them of Allaah and tell them that they will be held responsible before Allaah. You may also seek arbitration through wise and rational people from both of your families, as Allaah says (what means): {And if you fear dissension between the two, send an arbitrator from his people and an arbitrator from her people. If they both desire reconciliation, Allaah will cause it between them. Indeed, Allaah is ever Knowing and Acquainted [with all things].} [Quran 4:35]
Al-Kharashi said in Sharh Mukhtasar Khaleel (in the Maaliki School of jurisprudence) : "It means that the two arbitrators have to try to reconcile between the spouses with every means that could bring about affection and good marital relations between them. If this is not achieved, then they should study the case; if the abuse was from the husband, they should divorce her from him without taking anything from her, from neither her dowry nor anywhere else; and if the abuse was from her, they should entrust him to be just and have good marital relations with her; and if they decide that they should take compensation from her for him and effect the divorce between them, they may do so, if this is beneficial." [End of quote]
For more benefit, please refer to Fatwa 89039.
As regards you leaving the marital home, in principle this is forbidden except for a sound reason. So, if you can avoid the harm of his smoking, then you have to stay at home, but if you cannot repel this harm except by leaving home, then it becomes permissible for you to do so as a way of repelling harm. The Prophet, sallallaahu ‘alayhi wa sallam, said: "There should be no harm nor reciprocal harm." [Ahmad]
For more benefit, please refer to Fatwa 134654.
Allaah Knows best.