Is waiving money owed by a friend in fulfillment of a debt arising from the sale of his private merchandise and the embezzlement of its price, without informing him of the true reason for the waiver, considered repayment of the debt?

Your responsibility for the money is discharged as long as you have waived a fixed financial right of yours that he owes you, which is equivalent to or greater than the amount you took from him. You are not required to inform him of the original matter to avoid animosity and hatred.