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AIBU?

Share your dilemmas and get honest opinions from other Mumsnetters.

Original poster

To tell my brother in law that my sister is cheating ?

190 replies

Aurelie20 · 06/03/2020 19:19

I have been reading on this forum for months and now I have something I need advice on..

My sister and I are very close and always been. She is perfect ,have a perfect house , perfect children and a perfect husband... After my marriage ended I moved in with her , and since he works night shifts I spent a lot of time with him and the children during the day.

She told me about 2 weeks ago that she has been seeing a man for roughly a month and thinks about leaving her husband but wants some time with the other man to be sure. I AM SO SHOCKED! I can't believe her. She has a perfect man that loves her and does everything for her.

I am close to him and cannot at look him in the eyes now. Especially since he always talks about her. I feel like telling him because he does not deserve that. But at the same time I don't want to lose my sister. She trusts me. What would you do.

OP posts:
keeponandonandon · 07/03/2020 08:16

Why would you consider doing this to your sister? What she is doing is awful but if you tell her husband, you risk your relationship with your sister (forever) he will probably move on with his life and you wont see him very often, if ever. You also risk falling out with other members of your family as they will have opinions on this too, you also risk being excluded from your sisters childrens lives. Whether it's right or wrong, your family will feel the cannot trust you as they will be concerned that if you felt their actions are immoral, you would blurt it out. What about family gatherings, birthdays, Christmas etc. Your children are likely to suffer from the fallout from this if you open your mouth.

The consequences of this dilemma are enormous so, I would keep out of it and let your sister know you don't agree and move out.

butterpuffed · 07/03/2020 08:16

What you describe as perfect obviously isn't to your sister.

WeAllHaveWings · 07/03/2020 08:22

It's time for you to move out. Now.

Firstly so you stop spending so much time with Mr perfect, and so you aren't there when the shit hits the fan. They need space however this pans out.

Tell your sister exactly what you think of her behaviour, then tell her you don't want to hear anymore about her sleazy affair (telling you will be part of the thrill for her).

OhCaptain · 07/03/2020 08:28

I would:

Encourage sister to end affair and if she thinks there's anything of her marriage worth saving, to attend couple's counselling

If she won't end it, I would encourage her to tell him

I would NOT tell him myself while I'm living there with them while she's on the night shift

And I would move out ASAP. Because you're too close to this. And you sound jealous so you'll need to have a good think about your motives here.

PhilCornwall1 · 07/03/2020 08:29

Why would you consider doing this to your sister? What she is doing is awful but if you tell her husband, you risk your relationship with your sister (forever)

Must admit, if my brother told me he was doing this, I'd tell him exactly what I thought of him and not bother with him again, not that I do now anyway.

dodgeballchamp · 07/03/2020 08:34

Astounded by the responses here. Sharing DNA with someone doesn’t mean they shouldn’t be held to the same moral standard that a friend/acquaintance/general person would be, because otherwise where do you draw the line? Sister’s murdered someone, oh no you must keep quiet because it’s your sister? Bollocks to that. The whole eastenders style ‘faaaamily above all else’ is how things get brushed under the carpet when they really shouldn’t be.

In your position OP I’d move out ASAP. Then I’d tell your sister firmly and seriously that if she doesn’t tell her husband, you will. And follow through with it if she doesn’t come clean. I may cut her some slack if she ended the affair

vegansprinkle · 07/03/2020 08:35

She's your sister.

But I would encourage her to think very carefully

Freezingold · 07/03/2020 08:38

I’d move out too - the situation is toxic.

I’d urge your sister to tell him and I’d be very judgemental of her. My Ex cheated on me and it was part of overall abuse from him, cheating is abusive. His family brushed the cheating under the carpet as he was family, and basically enabled his abuse of me to continue.

saraclara · 07/03/2020 08:40

A lot of posters here are overlooking the fact that these sisters are really close, and that OP's sister had taken her in after her breakup.

What you might do regarding your own sibling who you don't much like/aren't that close to, doesn't really factor in to this thread. Maybe you don't care about a wider family break up that results, but OP. The sisters are close and live and trust each other.

So no, I don't think it's worth risking that for someone the OP will never see again. Talking to the sister is the way to go, not telling the BIL.

And likening having an affair to murder is just silly. This very much isn't an Eastenders plot.

saraclara · 07/03/2020 08:41

"...But the OP does."
(Missed a word)

Boshmama · 07/03/2020 08:41

Definitely stay out of it. And it sounds like you may have a crush on her DH - you sound quite jealous.

stairgates · 07/03/2020 08:43

Move out.

curlsnotfrizz · 07/03/2020 08:44

I would usually advice to tell the person that is being cheated on but seeing that it is family, I would butt out

agree with PP that by the sound of it, you seem to have a crush on him and your motivation to tell may not be as noble as you try to make it out.

PhilCornwall1 · 07/03/2020 08:44

She's your sister.

So? No one has a choice on their brothers or sisters. You are still allowed to dislike them and tell them that they are idiots through their actions.

dodgeballchamp · 07/03/2020 08:44

No of course having an affair isn’t comparable to murder but that’s the logical conclusion of the general stance of ‘never snitch on your family’. I have to agree with PP that I’d find it odd if the family took against OP if she did tell him, of course they’d want to help the sister during any ensuing breakup but I’d imagine it would be with a dose of ‘you brought this on yourself’. Also the husband is the father of OP’s nieces/nephews, who says she’ll never see him again?

Jeleste · 07/03/2020 08:51

I would never snitch on my sister/brother like that.
Tell her exactly what you think about it, move out and dont get involved any further.

YellowHighHeels · 07/03/2020 08:51

As it is your sister, in this particular instance I would not tell the husband as I would prioritise my relationship with her over doing the moral thing.

However, I would make it extremely clear to DSis that you think she should stop/ leave/ come clean. Whatever she needs to do to reduce making a fool of DH.

Yes PPs may be right and he may not be so perfect after all but that might not be true. Nice, decent, honest people get cheated on too so you need to do the right thing as far as you can whilst accepting that the nuclear option, telling him about the affair, might ruin your relationship with sister if she wanted to stay.

Move out too. It is shitty lying by omission to him whilst accepting his hospitality.

PersonaNonGarter · 07/03/2020 08:55

Get out of her house!

Don’t even contemplate doing this to your sister (and host). For all her faults, you really have yours.

Insideimsprinting · 07/03/2020 08:57

if you snitch on her

Christ are we all 10yr old!!!!!

If it's uncomfortable for you op you need to move out and let nature take its course.
My rule of thumb is that I won't interfere but for example in this instance I would tell her I won't say anything but if he asks I wont lie. I would go out spill the beans I would hope they can sort it between them bit I wo t be dragged into the lie either.

Insideimsprinting · 07/03/2020 08:59

That's supposed to say I wouldn't go snd spill the beans

YellowHighHeels · 07/03/2020 09:00

To add, regarding staying in their house, if he starts getting suspicious, he is likely to ask you what you know. Then you would have to either tell him or actively lie. That is a much harder position to be in than just being able to stay out of it.

pumpkinpie01 · 07/03/2020 09:07

I was in this predicament years ago except I didn't live with my sister. I was fully intending to keep out of it and then my BIL asked me to my face as he was already suspicious. I couldn't lie to him so the truth came out. Their marriage ended and nobody blamed me.

saraclara · 07/03/2020 10:05

No of course having an affair isn’t comparable to murder but that’s the logical conclusion of the general stance of ‘never snitch on your family

I haven't seen anyone say never snitch on your family. They have said don't snitch in this instance. For starters, having an affair isn't illegal.

My rule of thumb is that I won't interfere but for example in this instance I would tell her I won't say anything but if he asks I wont lie.

That sounds a very reasonable compromise.

KarmaStar · 07/03/2020 12:32

Hi op,
You do sound as if you are jealous of what your sister has and are rather too fond of your bil.
You can't hope she will run off with the om so you can step into her shoes surely?
Move out and rebuild a life for yourself and don't interfere in your sister's marriage.
There is a whole new world out there for you,it will be best for you if you take a step back.
It will also be better for your sister's family to have time alone.Can you work?take the first steps towards your future .

SlowDown76mph · 07/03/2020 12:36

You need to move out.