In the Kali-yuga, simply by accepting, the man accepts the woman as wife and the woman accepts the man as husband, that is the vow. Svīkāra eva hi udvāhe. Simply by acceptance. Because other things are not possible. And without marriage, that is not civilized life, because in the animal society there is no marriage. But in any form of civilized society there is marriage. Everyone has got sex appetite. Therefore, marriage is allowed by the Vedic system. And Kṛṣṇa says in the Bhagavad-gītā that dharmāviruddho kāmo 'smi, "Kāma, lust, which is not against religious principles, that is I am."
So marriage is essential. So far our society is concerned, we don't allow anybody to remain in our society as friends, girlfriend or boyfriend. No. They must be married. And these boys and girls, after being married, they are preaching nicely Kṛṣṇa consciousness. All my students who are married, they are doing preaching work more than sannyāsī. Yes. In the Kali-yuga, practically it is forbidden. Sannyāsaṁ pala-paitṛkam kalau pañca vivarjayet, aśvamedhaṁ gavālambhaṁ.