What should the wife do if she becomes anxious about her husband divorcing her over a past matter, such as him saying: "If my wife did such-and-such before our marriage, then she is divorced," and how can she ascertain if that occurred, and is she obliged to ask him?

The wife is not obliged to ask her husband whether he uttered conditional divorce or not, and she should not do so, because the original state is the continuation of the marriage contract. This behavior indicates that she is afflicted with obsessive whispering (waswasah), so she must ignore it.