Becoming like Christ is a journey. The forgiven fall sometimes and Lucifer then whispers in their ear that they've failed and lost forgiveness. That's not true. God doesn't care if you stumble. What He wants is for you to pick yourself up and start the journey again, leaving your sin behind. What is sin is accepting Christ and living life your way and ignoring sin. God sees man's heart and knows if he's truly repentant. Stumbling on the journey doesn't mean it's over.
Only one man never stumbled. Luckily He forgives us.