I meant not that it is adultery to divorce and marry another woman but that neglecting our wives to the point of divorce may be compared to adultery in a way. Like how lusting after another woman is committing adultery in our hearts.
Matthew 5:27 Ye have heard that it was said by them of old time, Thou shalt not commit adultery:
28 But I say unto you, That whosoever looketh on a woman to lust after her hath committed adultery with her already in his heart.
As for hardness of heart. We need to have a broken heart and a contrite spirit.
Isaiah 57:15 For thus saith the high and lofty One that inhabiteth eternity, whose name is Holy; I dwell in the high and holy place, with him also that is of a contrite and humble spirit, to revive the spirit of the humble, and to revive the heart of the contrite ones.