There is and always will be the issue of forgiveness. We all struggle with regret for past mistakes, and we all live with the memories of what we have done.
The first step in moving on is to admit that we are fallible and make mistakes. God forgives us, and we must, therefore, forgive ourselves and others.
Our problem can be letting go of our pride and embarrassment over what we have done. We should not be in a resentful place nor can we afford to be a person that holds resentment.
God encourages us to forgive, for it is in forgiveness that we are forgiven.
We also have to choose to not dwell on our mistakes. Sexual sin is often difficult to forget because of the intimacy we held with others. It did not seem like a bad idea at the time, but when the relationship dissolves, we face the regret of giving ourselves over to something temporary.
We have to choose to cast down our thoughts and imaginations. If we keep on allowing ourselves to dwell on our mistakes then we are going to be depressed. Choose to move forward.