TLDR; my SIL had an affair and then a few months after that started saying her husband had been abusive. I don’t believe her and feel that she has said these things just to convince her family that she should leave him and be with the affair partner instead.

This is a long story so apologies in advance. My (32F) fiancé (34M) and I have been together for over 10 years. In that entire time, his sister (32F) has been with her soon to be ex-husband (34M). They were together for 12 years total and have a 5 year old who is an absolute joy. They got married less than two years ago in June 2023, I was a bridesmaid, and it was such a happy day, at least from my perspective.

In July last year, somewhat out of the blue, my SIL started making noises about divorce. This was a bit shocking because they had obviously only been married just over a year and when asked what the problem was, she said that when she was working away she would come back and find the laundry wasn’t done (even though he’d been looking after their child, she was away for work a lot). I felt immediately that this wasn’t exactly a ground for divorce and something else must be going on.

In fairness to her, another thing that happened around the same time was on their first wedding anniversary he didn’t get her anything to mark the occasion. Now, he had given her a heads up that he didn’t have a lot of money that month and he would take her out when he got paid, but obviously he should have at least got her a card and some flowers or something. But I think in his mind they had discussed it and she was ok with it (he is male after all lol, no offence men…) either way, I guess I still felt this wasn’t enough to go straight to divorce after just a year, especially as they’d been together for 11 years before that and she knew what he was like… however, it felt like she was very serious but we were all quite unclear why.

Then a few weeks later she ended up coming clean that she had actually been having an ‘emotional affair’ with someone she worked with, and this was the reason she wanted a divorce, she really wanted to leave her husband and get together with her colleague…

BUT I don’t think she was banking on my MIL’s reaction - it could NOT have been worse. She was hysterical, there’s genuinely no other word for it. Like she would go on all the time about how she didn’t feel like she knew SIL anymore, she was ashamed of her, even saying she felt that my SIL was demonstrating narcissistic behaviour. She also HEAVILY pressured my SIL to stay with her husband and try to work on things, completely guilt tripping her about her child and how damaging the situation would be for him etc. I’m not saying I disagreed with everything, but I never thought she or anyone should be getting involved, and felt like it would all turn out worse in the long run if they stayed together after this - especially as my SIL told me at the time it all came out that she was only going to couples therapy to be seen to ‘try’ but she didn’t really want to and felt that she just had to go through the motions because it wouldn’t be worth the aggravation from her mum if she just walked away… I’m a child of divorce and know how toxic things can get so I told her straight up that it would be better for everyone to end it now if her heart wasn’t in it, but she didn’t listen. Her husband was devastated but wanted to work on things (they had only been married just over a year after all) so they went to couples therapy for a few months.

Throughout this time, her husband naturally had suspicions that she may not have actually ended this affair (as did I honestly but it’s not my business) - then a couple of months ago, in February, he found a letter from the guy which was dated from Christmas 2024 and in the letter the guy was talking about how at the same time next year they would be together ‘thinking about a mini-us’, saying the last year was the best year ever because he made her his etc etc. Like it was BAD. My SIL made up some shit about how she had cut him off and he sent her this just because he was pining or something but come on… it was obvious that she’d told the guy to hold on for a few months before she could split from her husband with less trouble. She also admitted to her family that she’d received multiple letters from the affair partner but she told her husband it had only been one letter, so she was even lying within the lie…

anyway, following on from this (and for a little while beforehand) my SIL had started saying things to my MIL about her husband that my MIL would say were ‘concerning’, things that had never come up before. I was told a few things which weren’t great, but from what I could tell had happened a looong time ago when they were much younger (and I’m not excusing everything based on age but, yknow, people grow and learn).

Once this thing with the letter came out, they obviously separated pretty quickly after that, and are currently in the midst of an increasingly acrimonious split and divorce process. Almost immediately, my MIL started telling my fiance and occasionally me, that my SIL’s husband was way worse than she had ever known and that my SIL has actually been in a controlling and coercive relationship for YEARS.

Now my main issue with this is if that’s the case, it’s very unusual because I know from both personal and professional experience that while people underreport and many victims certainly ‘downplay’ or ‘cover for’ perpetrators, that type of high level abusive behaviour rarely if ever goes entirely unnoticed by a victim’s friends/family.

One thing I can say with the utmost confidence is my SIL was in no way isolated. She lives around the corner from her parents and always has since her and her husband moved out, she was round at her parents almost every day and even more so since having a child, including many, many times on her own with just her mum or her parents… no one, absolutely no one, ever, thought anything abusive was happening and on top of that she never told anyone anything that would indicate that. Now ok, is that impossible? No. Is that unlikely? VERY. And maybe I’m wrong, maybe her husband was a covert narcissist and doing insidious things all along and we never noticed but I just find it hard to believe. Anything even somewhat concrete that I get told about these allegations still sounds kind of vague, or has no context etc. I feel like my SIL has distanced herself, we used to be very close but barely talk now, and that started a while ago. I’m not sure what it is, but I have this feeling that she doesn’t want to tell me things because I’m very good at sniffing out bs (I’m an investigator) and will be direct about things, I don’t think she wants to hear it or submit to any scrutiny, which I guess is fair enough - especially if she’s actually been through this - but as an investigator I’ve also learned to trust my gut on things and my gut is SCREAMING at me that she’s exaggerating a lot, if not making extremely damaging things up just to serve her own purposes... I feel like it has all been said now to pacify her mother that the right thing to do is leave her husband, with maybe the added benefit that her mum will tell the family to make everyone hate him. Everything me and my fiancé have heard about the supposed abuse is from his mum, not his sister directly, which I also find really weird considering we are (or were) all very close.

Anyway, there’s a lot more that I could say that’s gone on, but this is the basics. Am I an absolute asshole for being really skeptical about the allegations of abuse? She’s not taking it any further so this is all just within the family. I’ve no doubt that her ex is being incredibly petty now they are separated and probably acting out but I feel like in the context of her having an affair and then dragging him along for the last several months while likely continuing the affair in some capacity, he has a right to be angry and it’s understandable if he’s trying to make her life a bit harder rn, even if it’s petty… idk, am I wrong for thinking like this? Just to note, the affair partner is already back on the scene and was within like a week or two of them officially separating…