“Between God and us alone”? The social aspect of sin

Sacrament of Penance - Wikipedia
In the New Testament, Christians were admonished to "confess your sins to one another and pray for one another" at their gatherings (James 5:16), and to be forgiving people (Ephesians 4:32).[3]:322 But the "forgiveness of sins" in John 20:23 meant Baptism, which was entrusted to the disciples" and evidenced in the early Church (Acts 5:31; 3:19), with God and not the disciples forgiving the sins. "Binding and loosing" (Matthew 16:19; 18:15-18), in line with Jewish custom, did not pertain directly to the sin but to the person, who was excluded or admitted to the community (1 Corinthians 5:4-5; 2 Corinthians 2:7; Titus 3:10).[3]:321[4] In the New Testament there was no specific ritual for reconciliation except Baptism. With the delay of the expected Second Coming, there was a recognized need for a means of accepting back into the Christian community those who had been expelled for serious sins.[3]:321, 323

Does that mean rebaptism?

The future is heavily based on the past. Not just your past but everyone's past too. For example, somebody's restaurant review posted online influenced you to go there. Anyway, sin today influences future behavior.