The weight of carrying this secret while your friend trusts you completely must feel crushing, especially when the surgery was genuinely needed and urgent. Your friend's silence about the money might come from a place of care and understanding about your family situation, but living with this deception is clearly eating away at you. Consider having an honest conversation with him - acknowledging what happened and proposing a repayment plan might actually strengthen your friendship rather than destroy it, as it shows you value his trust over your own comfort.