'AITA for telling my SIL her strictly confidential information had already been leaked by her mom?' UPDATED

"AITA for telling my SIL that her 'strictly confidential' information had already been leaked by her own mother, which caused a massive family fight?"

My SIL holds a political office in the municipality where we live. During a conversation, she confided in me a strictly confidential piece of information, on the condition that I would not tell anyone, not even my partner, her brother. However, she also told me that she had shared it with her mother (my MIL), who was likewise not supposed to pass it on.

So for four days, the only people who were meant to keep this to themselves were my MIL and me. On the fourth day, today, there was going to be a meeting with the people concerned, and the information would be shared with them anyway. After that, it could also be “published” within the family.

So I promised her I would keep the information to myself, which I did.

Edit to add: It was a secret connected to her political position, but not "top secret". A strategic one that needed to be confidential for a couple of days.

(Another edit/small clarification: One commenter gave a good example of such a secret that I would like to quote. "It’s her secret though. Think, for example: I’m announcing my retirement Tuesday, or I’m announcing my bid for county council this week. The SIL’s own news, but not to be shared until a certain date (after the involved parties all know).

It makes sense that she might want to talk to close friends or family about her own decisions but doesn’t want word to get around too soon." So this is not about strictly confidential information whose disclosure would risk her position or even cause her to break an oath or the law, but it does have an impact on the community and the political environment.)

The day after our conversation, my partner (her brother) approached me and told me he had a secret piece of information to share. At first, I didn’t react. He kept talking, and it quickly became clear that he was referring to that exact secret. I interrupted him and said that I was already aware of it, without specifying what it was about.

I then asked him where he had gotten the information, and he said that his mother had told him. A few hours later, my SIL came to visit, and I let her know that unfortunately her mother had passed the secret on. She confronted her, and it led to a huge argument. After that, my partner confronted me and blamed me for the entire situation.

He says the family is now in conflict because I didn’t keep my mouth shut and told my sister-in-law that the secret had been shared. It’s also important to mention that during the confrontation, my MIL lied. First, she claimed she hadn’t told him anything. Then she said that her husband (their father, who, by the way, was not supposed to know either) had probably told him. Then she accused me of having told him.

Now I’m in a fight with my partner because he gave me confidential information that I wasn’t supposed to pass on, but I informed the original source of that confidential information that it had been shared. So basically my partner says I am the AH, because he told me the secret and I ran to SIL (the source).

AITA for feeling responsible to let my sister-in-law know that the information had been spread, which ultimately caused a huge fight?

(I would prefer not to have a discussion about whether it was responsible of my SIL to put me in this situation and tell me the secret. She doesn’t have many people to talk to, and she knows she can trust me. Sometimes you HAVE to talk to someone and share information in order to relieve pressure.)

Not long after posting, OP shared an update:

UPDATE
Business as usual. As if nothing had happened between my partner and me. Smiles, small talk, good mood.

That’s how conflict resolution always works here. Nothing gets resolved, it gets swept under the rug and ignored. Until it’s thrown back in your face in the next tense situation. So anyone who thinks I didn’t take my loyalty toward him seriously and that my poor "hubby" must be deeply hurt isn’t entirely right.

It’s difficult to include all the background details in an AITAH post, but I will say this much:
His loyalty toward me has always come last, whether it was about keeping promises, keeping secrets, or being faithful. I’m not saying this was an act of revenge for his behavior, but it certainly influenced my decision on a subconscious level.

Or rather, it’s probably the reason why my promise to his sister mattered to me, while I didn’t take my lack of loyalty toward him into consideration. Yesterday, after two missed calls from my MIL, I sent her a message telling her that I would not be discussing this situation any further. I think that would only create more room for arguments, and I simply don’t have the energy for it.

For years, I’ve suspected that I’m dealing with narcissists, my MIL and her son. His sister, on the other hand, takes after her father: she’s rather quiet, trustworthy, and handles things calmly. We’ll see how this unfolds. However, my SIL has already let me know that she intends to draw her own consequences and distance herself from the family in the near future. Guess who'll be held responsible for that lol

Here's what people had to say to OP:

oop_norf wrote:

"My partner confronted me and blamed me for the entire situation. He says the family is now in conflict because I didn’t keep my mouth shut."

I think it's pretty obvious that the family is in conflict because his mother couldn't keep her mouth shut, and you caught her and dobbed her in. If she'd kept SIL's confidence in the first place, then the wouldn't be anything to have a conflict about.

OP responded:

That's what I'm thinking.

ApprehensiveIce9026 wrote:

Is your husband aware that he is part of the problem? The SIL was the first wrong person, she wouldn’t have said to anyone. Then she told her mother, who told her husband and her son, who told you. There’s too much gossip in this family. Your husband is being too much of a mama’s boy from my perspective, he rather blame you than see his mom as the real wrong one.

OP responded:

This is exactly the way I see it, actually.

DeciduousEmu wrote:

It's obvious that your MIL has always been an "I'm never wrong" type of person. Undoubtedly, your husband (and probably the rest of his family) has been conditioned his entire life to do whatever it takes to keep her happy so as not to face her wrath.

Here is a good post that explains how entire families can be conditioned to constantly take steps to appease the person who is the actual problem in the family. It is possible that SIL was finally fed up with MIL being a chronic liar and actually set this scenario up to test her mother.

SIL was wise enough to know that you wouldn't "let this slide" as opposed to your husband who would have said nothing to make sure he didn't "rock the boat". This is evidenced by his reaction of trying to blame someone other than his dear sweet mother. If SIL did manufacture this scenario, good for her. It was not entrapment. It was exposing MIL for the selfish b***h that she is. NTA.

OP responded:

Well, you're hitting the nail right on the head. Afterward, she let me know it was kind of a test to see if she could trust her. And now MIL says everybody is making " a mountain out of a molehill.”

Rude-You7763 wrote:

You’re literally the only one that is NTA. Your MIL told your husband and potentially her husband when she wasn’t supposed to tell anybody and then lied about it and tried to blame you so it’s pretty obvious why she’s the AH.

Your husband shared a secret that he wasn’t even supposed to know and then blamed you for telling the truth so he’s obviously also an AH. Depending on the secret, your SIL might also be an AH but without more context I can’t say for sure.

SheRa7 wrote:

SIL failed to follow Gibbs' Rule #4: The best way to keep a secret? Keep it to yourself. Second best? Tell one other person - if you must. There is no third best.

You are NTA. Your husband OTOH is most definitely an AH.