Roman legislation set two conditions that were necessary for justae nuptiae, or marriage, to exist in a valid form. These elements were cohabitation, or having the wife reside at the husband's house and be at his disposition at any given time, and the element of affectio maritalis.
The term seems pretty self-explanatory, right? Marital affection. Yet this doesn't exactly entail the meaning that the modern concept of "affection" has. The affectio maritalis was actually the intention that the partners had to be husband and wife, which was expressed through their social and intimate behavior.
The affectio maritalis had three elements:
Nomen, or name, which was the wife taking her husband's gens name;
Tractatus, or treatment, which involved the husband formally treating his wife as a wife, in public and in intimacy, and viceversa;
and finally, Fama or reputatio, which involves society's knowledge of them being husband and wife.
The withdrawal or defect of the affectio maritalis meant an ending of the marriage. This was also the case when either the wife or husband fell captives of war, and eventually regained their freedom through the ius postliminii and returned to his home, since the affectio maritalis is a de facto situation, not de jure, this being due to the situation being born from a law, yet depending its existence on fact, and this fact had been interrupted by said captivity.