How does a young man balance his desire to marry a religious and distinguished girl whom he loves, but who is an orphan, suffers from a heart condition, and cannot bear children, with his mother's absolute refusal of this marriage?

It is Islamically forbidden to establish a relationship between a man and a non-mahram woman because of the temptation involved. It is disliked to marry a woman who is not fertile, as this defeats the purpose of increasing progeny. This prohibition is on the basis of dislike, not strict prohibition, and a man may regret in the future not having children. An adult man is not obliged to obey his parents in marrying the woman they choose, but it is not advisable to disobey parents, as this may cause estrangement and conflict, especially if their objection is valid, such as the girl's illness or inability to conceive. If a man pledges to marry a girl, he is not obligated to fulfill this pledge, as it is merely an non-binding engagement. If he had sworn an oath or made a covenant with Allah to do so, he must offer expiation for breaking an oath.