The Third is the Shaytaan
Rasul Allah (sal Allahu alaihi wa sallam) said: “Whenever a non-mahram man and woman meet in seclusion, Shaytaan definitely is the third one joining them.” [Tirmidhi]
What this hadith means is that Shaytaan arouses their passions and incites them to commit evil. Prevention is better than cure. Fornication and adultery rip to shreds the psychological health of society. Since the family is the building block of society, for a society to be healthy, it must have healthy families that constitute it.
To prevent any situation arising which might harm the family unit, Islam nips the source of problems in the bud. A person is responsible not only for himself or herself but for the spiritual, emotional, psychological and physical well being of their children as much as it is in their control. From their children will arise many more generations. Keeping this in mind we have to do our best to provide as healthy a moral environment as we can so we are not held responsible for the destruction of future generations.
“If the breakdown of the family and female security is to be averted, only two strategies are available: firstly, members of society may be conditioned to believe that sexuality is from the devil, and should inspire feelings of guilt and distaste; or secondly, sexuality may be accepted as the loving expression of a natural human need, in which case the sexes must be separated, within reason, to avoid the risk of the temptation of weak souls and hence their unchastity.”
“Historically, the first of these two choices has been that of Christianity, while Islam has opted for the second. The modern Western attitude, in which there is both an obsession with sexuality and a casual mingling of men and women, and which has resulted in massive promiscuity (and hence infidelity, divorce, abortion and disease) does not represent an ethically coherent system.” [The Seventy-Seven Branches of Faith, translator’s note, The Quilliam Press]