Psalm 41:9 contains a verse Jesus specifically cited about his own betrayal: "Yea, mine own familiar friend, in whom I trusted, which did eat of my bread, hath lifted up his heel against me." The Hebrew akal — "eat of my bread" — is the language of table fellowship, covenant intimacy. The sting of betrayal in this verse is its intimacy. Jesus quoted it about himself. The wound of betrayal from inside a close relationship has been experienced by the Son of God. It is not foreign to God.
Proverbs 4:23 — "Keep thy heart with all diligence; for out of it are the issues of life" — gives the structural principle for life after betrayal. The Hebrew mishmar — "diligence" — means vigilance, watchfulness, guard. Protecting the heart after betrayal is not the same as closing it off. It is the active, discerning work of knowing what to let in and what to keep out.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.