Question
Clarification regarding adultery, extra-marital relations
Answer
Mutual consent does not make the actions allowable or moral. Thieves may mutually agree on robbing someone and not each other, but it does not make their actions either moral or allowable. Such actions as you describe are condemned by all the scriptures. Swami Nikhilananda in his writings on Hindu ethics says:
Besides the objective duties based on the castes and stages of life, there are laid down the common duties of men, the sadharanadharma, which are the foundation of the moral life. Manu, the lawgiver, enumerates these common duties as follows: steadfastness (dhairya), forgiveness (kshama), good conduct (dama), avoidance of theft (chauryabhava), control of the senses (indriyanigraha), wisdom (dhi), learning (vidya), truthfulness (satya) and absense of anger (akrodha)...the aim of Hindu ethics is to enable a man ultimately to conquer his lower self and attain freedom from passion, desire, and attachment.
All Hindu philosophers regardless of their conceptions of the supreme end of man, admit the empirical reality of the individual, endowed with volition, desire, will, conscience or consciousness of duty, emotion, etc. The goal of Hindu ethics is to train these faculties in such a way that they shall lead the individual to the realization of Moksha, or Liberation. Therefore all the schools of philosophy have described the virtues and their opposites in detail. It is expected of the moral agent that he should follow the former and shun the latter. We propose to discuss the virtues and their opposites according to the classification of Nyaya and of Patanjali's system.
Vatsyayana, in his commentary on the Nyaya aphorisms, classifies will as impious (papatmika) and auspicious (subha). The impious will leads to unrighteousness (adharma), and the auspicious will, to righteousness (dharma). Righteousness, it is necessary to add, is conductive to the Highest Good, whereas unrighteousness produces evil. The purpose of ethics is to subdue the impious and to manifest the righteous will.
Unrighteousness may take three forms, namely, physical, verbal, and mental, depending upon the condition of its functioning. Physical unrighteousness manifests itself asa cruelty (himsa), theft (steya), and sexual perversion (pratisiddha maithuna); verbal unrighteousness, as falsehood (mithya), rudeness (katukti), insinuation (suchana), and gossip (asambaddha); mental unrighteousness, as ill-will (paradroha), covetousness (paradravyabhipsa), and irreverance (nastikya).
Patanjali...describes the virtues that must be cultivated...chastity or continence...
The practice of continence, highly extolled by all the philosophers and mystics of India, implies, besides the literal meaning of the vow, abstention from lewdness in thought, speech, and action through any of the sense-organs. Through the practice of this virtue, one develops the capacity for subtle spiritual perception.
Krishna says in the Gita (chapter XVI. 4-12):
Ostentation, arrogance, and self-conceit; anger, rudeness, and ignorance--these belong to him who is born to the heritage of the demons.
Men of demonic nature know not what to do and what to refrain from doing. Purity is not in them, nor good conduct, nor truth.
They say: "The world is devoid of truth, without a moral basis, and without a God. It is brought about by the union of male and female, and lust alone is its cause: what else?"
Holding such a view, these lost souls of little understanding and fierce deeds rise as the enemies of the world and its destruction.
Giving themselves up to insatiable desires, full of hypocrisy, pride, and arrogance, they hold false views through delusion and act with impure resolve.
Beset with innumerable cares, which will end only with their death, looking on the gratification of desire as their highest goal, and feeling sure that this is all;
Bound by a hundred ties of hope, given up wholly to lust and desire,...
and in verse 16:
...addicted to the gratification of lust, they fall into a loathsome hell.
and in verse 19-21:
These cruel haters, these evil-doers, these vilest of men, I hurl always into the wombs of the demons in the cycle of births and deaths.
Having fallen into the wombs of the demons and being deluded from birth to birth, they never attain Me, O son of Kunti, but go further down to the lowest state.
Three are the gateways of this hell leading to the ruin of the self--lust, wrath, and greed. Therefore let man renounce these three.
and in verses 23-24:
He who discards the injunctions of the scriptures and acts upon the impulse of desire attains neither perfection nor happiness nor the Supreme Goal.
Therefore let the scriptures be your authority in determining what ought to be done and what ought not to be done. Having learnt the injunctions of the scriptures, you should do your work in the world.
Note: “The question: Clarification regarding adultery, extra-marital relations” is licensed by Stack Exchange Inc (https://hinduism.stackexchange.com/); user contributions licensed under CC BY-SA.