What is the legitimate stance if the husband does not marry after swearing, "You remain unlawful to me if I do not marry another woman besides you," and is this oath of his considered a divorce oath or not, and what is the expiation consequent upon that?

If the husband's oath implies the prohibition of his wife to him unless he marries another, then his intention is to be considered: if he intended divorce, it is a divorce; if he intended ẓihār (a form of injurious vow), it is ẓihār; if he intended an oath by Allah, he must offer expiation for an oath (kaffārat yamīn); and if he intended nothing, he must offer expiation for an oath.

Since the oath was in a form of breaking it, according to the Hanafis, nothing is binding on him unless he despairs of marrying. According to the Malikis, if he intended divorce, he is prevented from marital enjoyment until he marries. Here, it is permissible to follow the Hanafi school, so nothing is binding on the husband until he is certain of his despair of marrying.

If the husband had previously divorced his wife once, he still has two divorces remaining, not just one.