Does the pain and sorrow resulting from an illicit relationship have value to Allah as atonement, or is it merely a punishment for the sin?

Grieving over a missed sin is a transgression, because it contradicts repentance, among whose conditions is regret for committing the sin, not for missing it. However, if this grief persists after a sound repentance, then it becomes one of the calamities that expiate sins or elevate ranks.