What if I can't forgive?

When I was younger, under 10 years of age, I was sexually molested and abused by a family friends son. I ran into him at school store a few weeks ago and I literally wanted to tear him apart. However, his parents were there. Before I saw him, I had worked on forgiveness. I prayed for him and tried to ask God to help and bless him. I tried to move on. I prayed for God to intervene in my life to forgive him and move on. Then I saw him. How can I be a Christian if I can't forgive? This kills me inside because I feel I'm failing as a Christian.
What if I can't forgive?
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