Catena Aurea on Matthew 5:32: Augustine of Hippo

Nothing can be more unjust than to put away a wife for fornication, and yourself to be guilty of that sin, for then is that happened, “Wherein thou judgest another, thou condemnest thyself.” [Rom 2:1] When He says, “And he who marrieth her who is put away, committeth adultery,” a question arises, does the woman also in this case commit adultery? For the Apostle directs either that she remain unmarried, or be reconciled to her husband. There is this difference in the separation, namely, which of them was the cause of it. If the wife put away the husband and marry another, she appears to have left her first husband with the desire of change, which is an adulterous thought. But if she have been put away by her husband, yet he who marries her commits adultery, how can she be quit of the same guilt? And further, if he who marries her commits adultery, she is the cause of his committing adultery, which is what the Lord is here forbidding.