This is an example only and the reader should apply the principle to their own possible situation, actual or imagined.
Your daughter’s partner has a secret bank account for the purpose of gambling on the races about which your daughter is unaware. One day he mentions this to you in the course of a relevant conversation and asks you to keep it secret. Some time later the relationship disintegrates and remains that way.
For how long do you maintain the secret entrusted to you?