Adam Clarke on Psalms 41:9

Mine own familiar friend - This is either a direct prophecy of the treachery of Judas, or it is a fact in David's distresses which our Lord found so similar to the falsity of his treacherous disciple, that he applies it to him, Joh 13:18. What we translate mine own familiar friend, איש שלומי ish shelomi, is the man of my peace. The man who, with the שלום לך shalom lecha, peace be to thee! kissed me; and thus gave the agreed-on signal to my murderers that I was the person whom they should seize, hold fast, and carry away.

Did eat of my bread - Was an inmate in my house. Applied by our Lord to Judas, when eating with him out of the same dish. See Joh 13:18, Joh 13:26. Possibly it may refer to Ahithophel, his counsellor, the man of his peace, his prime minister; who, we know, was the strength of Absalom's conspiracy.