Does his wife become forbidden to a man if he says to someone: "My wife is forbidden to me if I do not pay off your debt," and he is unable to pay off the debt after the agreed-upon period?

If two weeks have passed and the debt has not been paid, then the oath has been broken. Regarding the prohibition of your wife, it depends on your intention, whether you intended zihar, divorce, or an oath. This is the preponderant view among the jurists. One must be careful not to be lenient in using such phrases, which can put a person in a difficult situation and disrupt family unity.