Is swearing by "By God, if I find out that you are smoking shisha with your friends, that will be the the last day of us living together" considered a divorce, and does it require expiation, and what should the husband do towards his wife who secretly smokes shisha with her friends, and should he leave the house because of "bad neighbors"?

Divorce does not occur merely by discovering the wife's smoking, nor is it obligatory to divorce her. However, an expiation (kaffarah) by an oath to Allah is required for not divorcing her.

The wife must be prevented from smoking in accordance with the husband's guardianship (qawamah), and she must obey you in refraining from befriending bad neighbors and not allowing them into the house or going out to them without your permission.

If the wife does not obey, then means of reform should be followed: admonition, abandonment in bed, then non-violent beating.

And if the husband fears for his family from bad neighbors, it is better to live among righteous neighbors.