Does a husband's statement to his wife, "You are forbidden to me," constitute a divorce under duress, given his lack of intention to divorce, and then he returns to his forbidden act?

If the husband intended by prohibiting his wife merely to appease her, then only an expiation for a broken oath (kaffarat yamin) is required of him. One should be cautious of using words of divorce or prohibition to solve marital problems. The husband must offer sincere repentance if he is in a relationship with a woman unlawful to him.