It seems to me that the issue now is not so much forgiveness as it is reconciliation. Your fear likely is the result of a lack of trust toward the person because of the betrayal. Reconciliation has to be earned. Have you talked with the person and has this person understood the offense and now is willing to change? You need to build some confidence in this person’s behavior and this will come if the person begins to behave in a way as to earn your trust.
Learn more at What Forgiveness Is Not.