Does divorce occur when a husband breaks an oath he swore not to watch pornographic films? And do the divorces multiply with repeated viewing? And are expiation and informing the wife obligatory?

You have not clarified the wording of the oath. If you swore by Allah or by the Qur’an, and you did not swear by divorce, then you owe a single expiation for breaking an oath (feeding ten poor people, or clothing them, or fasting for three days). The expiation does not repeat with the repetition of breaking the oath unless it was in a wording that necessitates repetition.

However, if you swore by divorcing your wife, then the fatwa we adopt is that a single divorce occurs upon breaking the oath, unless it was in a wording that necessitates repetition. You are not required to inform your wife of what has happened. Some scholars, like Ibn Taymiyyah, are of the view that divorce does not occur as long as you did not intend divorce with this oath, but you are still obligated to pay an expiation for breaking an oath.

It is obligatory to hasten to repent from watching forbidden things and to conceal your sin.