Dear Peter:

As I understand it the boy is being forced to "re-lived" past sin in his dreams. That being the case, and presuming he has already confessed those sins, there is no need to return to the Sacrament of Confession. It can be a demonic agenda to get the boy to doubt his faith and the promise of God to wipe out of existence forgiven sins of the past.

While I do not believe demons can know our absolved past sins, they can manipulate our imaginations in such a way that causes doubt. The boy then will come up with some sins upon his own knowledge, not the demon's. This can make it look like the demons have knowledge of forgiven sins when they actually do not. As we say here in Iowa, there is more than one way to skin a cat.

This is the same way that con artist psychics can appear to know things things they do not actually know. A question from a demon to inspire the boy to remember some past sin can be like, "boy, you remember that sin of lust. Are you sure you are forgiven?" A con artist is pretty safe in asking such a question because almost everyone lusts and doubt is a common human experience. The question may conjure in the boy's mind a specific incident where he lusted. This is how con artists work to seem to know something they do not, and demons are the king of con artistry.

Thus, the attack is not that the demon is making the boy re-live some forgiven sin the demon knows about, it is rather perhaps an attack to the imagination to doubt and tricking him to think about it and thus re-live it. I believe the boy, on this score, is perhaps being attacked by a spirit of doubt.

If the boy is re-living some past sin that he has not confessed, then yes, he should confess it.

God Bless,
Bro. Ignatius Mary