Did the husband err in his decision to marry a second time due to the non-fulfillment of his sexual desires, and what is your advice to him to avoid Allah's wrath, and how can he repent from his oath not to marry again?

The wife must make herself available to her husband. If she refuses without a valid excuse, she commits a sin. If your wife does not help you maintain your chastity, you are permitted to marry another woman, provided you observe justice, and she has no right to prevent you. You should try to convince her about the second marriage. If she insists on refusing and demands a divorce, and you cannot endure the situation, then divorce her, because obedience to Allah takes precedence. Regarding the oath not to marry another woman over her, it is binding, but you can expiate it (by feeding ten poor people, or clothing them, or freeing a slave; if unable, then by fasting for three days).