Let's say a person has been cheated on, but the cheating already happened a long time ago (for example, around 15-20 years ago)

If you were the person cheated on, would you just let it go, or would you treat it the same as if you were cheated on yesterday?

Would there be any aggravating or mitigating factors which would help you decide on how to approach the scenario?

This hasn't happened to me personally, so it's hypothetical from my perspective