Jamieson, Fausset and Brown on 2 Samuel 17:23

23. when Ahithophel saw that his counsel was not followed--His vanity was wounded, his pride mortified on finding that his ascendency was gone; but that chagrin was aggravated by other feelings--a painful conviction that through the delay which had been resolved on, the cause of Absalom was lost. Hastening home, therefore, he arranged his private affairs, and knowing that the storm of retributive vengeance would fall chiefly upon him as the instigator and prop of the rebellion, he hanged himself. It may be remarked that the Israelites did not, at that time, refuse the rites of sepulture even to those who died by their own hands. He had an imitator in Judas, who resembled him in his treason, as well as in his infamous end.