No, you don’t have to reveal past sins to te party that was sinned against.
You can tell the person if one wants, but it’s not really necessary. In some instances, it would even be detrimental.
In 12-step programs, they recommend making amends for past mistakes, but only if to do so would not cause further harm. I think it’d be prudent to use that as a guideline.
In many, if not most, cases, it’s not helpful to bring up past sins which can’t be undone.
If amends can be made, with or without the person’s knowledge, it would need to be weighed carefully if this would be more beneficial or harmful to reveal past sins.