Can A Person Make Such Oath/Swear
Islam does not forbid a person from making a personal commitment for the sake of their marriage. Promising your wife that you will not marry again is a personal and moral pledge, not a declaration that polygamy has become haram. What is haram is to claim that Allah has forbidden something He has allowed. Choosing not to use a halal option out of responsibility, love, or commitment is completely permissible. Such a promise is treated as a condition or ethical commitment, and breaking it would be a matter of breach of trust, not invalidity of the second marriage. If it was made as an oath, then breaking it would require kaffarah, not sinning by marrying again. Islam separates divine law from personal promises, and as long as this distinction is maintained, making such a commitment is Islamically and logically sound.