Sforno on Numbers 5:31/ספורנו על במדבר ה׳:ל״א

1ונקה האיש מעון, even though he had suspected his wife’s fidelity. The reason is that by her conduct she had given him just cause for such suspicions. Had she not ignored his warnings things would not have come to such a pass. We have our sages in Shabbat 56 on record that David did not accept badmouthing which was designed to make Mephiboshet appear as having been disloyal to him. He rather based himself on visual evidence. [This was Sh’muel’s interpretation of what had occurred. Rav disagrees with his assessment. Ed.]

2והאשה ההיא תשא את עונה, that if she had been guilty of adultery she would die, and if not, her public embarrassment at undergoing the procedure as a punishment for having had the effrontery to ignore her husband’s warning would be her punishment.