I think this is the biggest obstacle in living a Christian life. Somehow it is easier to accept (with grace) the suffering that is a result of acts of God, like health issues, circumstances beyond our control and even the actions of others. The hardest suffering to accept is the suffering we bring on ourselves. Somehow regretting those things seems more noble; to forgive ourselves seems as if we are saying what we did is okay.
This is simply not the case. It is mistaken thinking. Regret is the roadblock to grace. It is a brick wall that we build between God and God's infinite and unconditional love for us.
Sometimes we get to make restitution to those we have harmed. Sometimes that is simply not the case. Sometimes the people hurt by our actions forgive us; sometimes they don't and may not ever do so. Either way, we know we must confess our sins and ask God to forgive us.
As Catholics, we have an unusual privilege. We get to take our sins to the confessional and receive absolution right then and there; we get the privilege of hearing the voice of the priest telling us out loud that God has forgiven our sins. God has forgiven us, unconditionally, no holds barred. Reconciliation is a full circle.
Therefore, we must now forgive ourselves. We must do this because not doing so is to turn our back on God's grace. That, in itself, is a sin. God is saying to us, "You have a beautiful heart. You made a mistake and you are forgiven."
When we do this hard thing, when we say, "Yes, Lord, I am loved by you, not in spite of my flaws but because of them," we allow God's beautiful work to begin in us. Some of my most humiliating lessons have been the most powerful; once I let go the humiliation, then my heart is open and I am able to be taught. And those lessons are the ones we never forget.. Nouwen says it so well:
I kept running around it large or small circles always looking for someone or something able to convince me of my Belovedness.
Self rejection is the greatest enemy of the spiritual life because it contradicts the sacred voice that calls us the "Beloved." Being the Beloved expresses the core truth of our existence.
Henri Nowen, Life of the Beloved: Spiritual Living in a Secular World
Therefore, we must forgive ourselves. Such is our work and our duty and that work is what paves the road to grace. We must claim our belovedness and open ourselves to the abundant and overflowing grace available to us.