(Proverbs 7:27 KJV) Her house is the way to hell, going down to the chambers of death.
The action being discussed here is sexual sin. For the young man it is fornication, for the woman, adultery. They are both sin, plain and simple. It is not a matter of sex before marriage being okay and cheating on your spouse isn’t. It is not okay to violate God’s call to sexual purity as long as you are really in love. People “living together” have one foot in the grave and don’t even know it. I have a hard time believing they don’t know it but I guess if I can convince myself that the apple fritter I just ate won’t really make a difference then their appetites can give them the excuses they need to live in denial.
So? God cares about how we live. Sexual behavior is part of the deal. Live upright and righteous. Don’t make excuses; God doesn’t.