Whether inseparableness of the wife is of natural law?

Objections

Objection 1 : It would seem that inseparableness of the wife is not of natural law. For the natural law is the same for all. But no law save Christ's has forbidden the divorcing of a wife. Therefore inseparableness of a wife is not of natural law.
Objection 2 : Further, the sacraments are not of the natural law. But the indissolubility of marriage is one of the marriage goods. Therefore it is not of the natural law.
Objection 3 : Further, the union of man and woman in marriage is chiefly directed to the begetting, rearing, and instruction of the offspring. But all things are complete by a certain time. Therefore after that time it is lawful to put away a wife without prejudice to the natural law.
Objection 4 : Further, the good of the offspring is the principal end of marriage. But the indissolubility of marriage is opposed to the good of the offspring, because, according to philosophers, a certain man cannot beget offspring of a certain woman, and yet he might beget of another, even though she may have had intercourse with another man. Therefore the indissolubility of marriage is against rather than according to the natural law.