I have always thought that this was a curious phrase, "Be not bitter against them." And I thought that it was interesting that wives were not similarly instructed. Can't wives be bitter too?
To "be bitter" "with them" (McCord's) or "against them" (ASV, KJV) indicates not only the bitter feeling on the part of the husband but apparently bitter or harsh (NIV) treatment of the wife.
I am made to think that "bitterness" is a greater problem with men, both in attitude and in action. Why the bitterness? Of course it could be a failing of the wife (what wife/human is perfect? But hubby, you aren't either!). Could it be the personal failings of the husband that are taken out on the wife? Could it be the personal disappointments that the husband faces? Could it be the demands and responsibilities of the family that are upon the shoulder of the husband that the husband finds difficult to fulfill? Could it be the sacrifice of many things in life in order to have a wife and family that he has been unwilling to make but forced to make?
And perhaps you are thinking, "I would never be bitter toward my wife, nor treat her in a harsh manner." And I hope not, too. But if you considered the instances of divorce where there was no adultery, I would not be surprised if the majority were women divorcing their husbands because of the harsh way the husbands treated them. - I said majority - NOT all and that is from my observation. It is not from a social-science study. As a whole, men need to do better.
The antidote to "bitterness" is found in Ephesians 5:28-29. There Paul placed a great emphasis on love being sacrificial and a desire for the good of the wife (Ephesians 5:25-29). The husband chooses this. Ultimately, we choose to love and treat our wives in a loving manner. Choose. Choose not to be bitter. Choose to love your wife.