Mufti says: A man despite of divorcing his wife keeps her in his house without halaala saying that we have reached a compromise. However, everybody knows that after three divorces a woman is no more the husband’s wife and is haram on the man. Such a relationship is equivalent to having an illegitimate relationship with a woman.
The only solution to having the woman who you have once divorced is through halala and that also if the halala is not done intentionally.
What happens in our society is that Zina is openly being committed, God forbid, if later a child is born, his lineage can also not be drawn from his father because the woman he has had a child with was now haram on him. Such people are not going to attain anything in this world or the Hereafter. And Allah knows best.