It isn't always enough to be forgiven by others. Sometimes you have to learn to forgive yourself.
Forgiving oneself is not easy; but the good news is that peace of mind is a result of doing so. Talk with God about your sin in prayer and ask for His forgiveness. This is the first step in finding the path to forgive yourself.
To give his people knowledge of salvation through the forgiveness of their sins,
Luke 1:77 (NABRE)