Keeping confidence or lying by omission

[GeorgeClarkefan]

Where do you draw the line in your marriage between keeping a confidence or lying by omission?

My husband has kept a secret for nearly five months.

To be fair it doesn’t really affect me but I am still upset.

OP, if your husband's sister asked him to keep her news confidential, then obviously he can't tell anyone - that includes you, and has nothing to do with being "family".

If I told you as a friend that I had won £1 million pounds on the Lottery, but you must keep it confidential, I would be furious if you told your husband, and would probably end the friendship. See? That's how it works.