David wrote Psalm 41:9 from the raw experience of betrayal. "Even my close friend in whom I trusted, who ate my bread, has lifted his heel against me." To lift your heel was an ancient gesture of contempt — a deliberate act of disloyalty from someone who had been trusted, welcomed at your table, considered a friend.
Jesus quoted this verse in John 13:18, speaking of Judas. Though with one significant difference: Jesus did not say "my close friend in whom I trusted," because He knew Judas's heart from the beginning. But the experience of betrayal — the one who shared bread turning against the host — was identical.
If you have been betrayed by someone you loved and trusted, you are in the company of David and of Jesus Himself. That is not a small thing to know.
What do you do with it?
David does something instructive. He doesn't minimize it. He doesn't pretend it didn't happen. He puts it honestly before God. And then he says, in verse 10, "you, O LORD, be gracious to me." Not: punish them. Not: make it right immediately. Be gracious to me. In the face of betrayal, he runs to grace.
Forgiveness is not forgetting. It is not pretending the injury wasn't real. It is releasing the debt — not because the person deserves it, but because you have been forgiven infinitely more than you could ever be owed.