It is always valuable to look at the 'first mention' of any subject in the scriptures. Most, but not all, subjects are introduced in Genesis and then wrapped up in the book of Revelations.
The first 'other woman' scenario we see in the Bible is in Genesis chapter 16 with Abraham, Sarah and Hagar.
"Now Sarai, Abram's wife, had borne him no children. She had a female Egyptian servant whose name was Hagar. And Sarai said to Abram, 'Behold now, the LORD has prevented me from bearing children. Go in to my servant; it may be that I shall obtain children by her.' And Abram listened to the voice of Sarai. So, after Abram had lived ten years in the land of Canaan, Sarai, Abram's wife, took Hagar the Egyptian, her servant, and gave her to Abram her husband as a wife. And he went in to Hagar, and she conceived. And when she saw that she had conceived, she looked with contempt on her mistress. And Sarai said to Abram, 'May the wrong done to me be on you! I gave my servant to your embrace, and when she saw that she had conceived, she looked on me with contempt. May the LORD judge between you and me!' But Abram said to Sarai, 'Behold, your servant is in your power; do to her as you please.' Then Sarai dealt harshly with her, and she fled from her. The angel of the LORD found her by a spring of water in the wilderness, the spring on the way to Shur. And he said, 'Hagar, servant of Sarai, where have you come from and where are you going?' She said, 'I am fleeing from my mistress Sarai.' The angel of the LORD said to her, 'Return to your mistress and submit to her.' The angel of the LORD also said to her, 'I will surely multiply your offspring so that they cannot be numbered for multitude.' And the angel of the LORD said to her, 'Behold, you are pregnant and shall bear a son. You shall call his name Ishmael, because the LORD has listened to your affliction. He shall be a wild donkey of a man, his hand against everyone and everyone's hand against him, and he shall dwell over against all his kinsmen.' So she called the name of the LORD who spoke to her, 'You are a God of seeing,' for she said, 'Truly here I have seen him who looks after me.' " - Genesis 16:1-13 ESV
Wow, There is so much here isn't there? Human nature is on display. God's love and mercy is also. Men and women make bad decisions out of need but God is merciful to us.
The last mention is darker. Society itself has become adulterous.
"Then one of the seven angels who had the seven bowls came and said to me, 'Come, I will show you the judgment of the great prostitute who is seated on many waters, with whom the kings of the earth have committed sexual immorality, and with the wine of whose sexual immorality the dwellers on earth have become drunk.' And he carried me away in the Spirit into a wilderness, and I saw a woman sitting on a scarlet beast that was full of blasphemous names, and it had seven heads and ten horns. The woman was arrayed in purple and scarlet, and adorned with gold and jewels and pearls, holding in her hand a golden cup full of abominations and the impurities of her sexual immorality. And on her forehead was written a name of mystery: 'Babylon the great, mother of prostitutes and of earth's abominations.' And I saw the woman, drunk with the blood of the saints, the blood of the martyrs of Jesus. When I saw her, I marveled greatly. But the angel said to me, 'Why do you marvel? I will tell you the mystery of the woman, and of the beast with seven heads and ten horns that carries her... And the angel said to me, 'The waters that you saw, where the prostitute is seated, are peoples and multitudes and nations and languages. And the ten horns that you saw, they and the beast will hate the prostitute. They will make her desolate and naked, and devour her flesh and burn her up with fire, for God has put it into their hearts to carry out his purpose by being of one mind and handing over their royal power to the beast, until the words of God are fulfilled. And the woman that you saw is the great city that has dominion over the kings of the earth.'' - Revelation 17:1-7, 15-18 ESV
This 'other woman' concept shows the systemic failure of the natural person to cope with their needs apart from God. Problems compound into even more complex problems with a victim until the system consumes itself in the end.
But there is hope. God is merciful and has a merciful provision for the individual. The system... not so much.
Hagar found out she was not God's 'other woman.' He had a loving provision for her.