My sister is the OW and I’m not sure what to do

[Namechange420666]

Title says it all really, but I will provide some background information.
My sister is 35, I am 25. I am closer to my brothers, but when I was young she used to babysit me a lot and often took care of me (paid), so we are kind of close. Probably a bit closer than average siblings with a big age gap. I love my sister dearly, but she can be difficult. She’s always had this thing about me being the favourite and my dad never loved her, and sometimes I get a bit sick of hearing about it. Other than that she’s overall a nice person (well I thought she was, this is making me question it.)
Today I went to lunch with her. She seemed excited and happy which was great since she has been a bit down recently. She was telling me about her new boyfriend and all was good. I suggested she brings him to a party I’m hosting in June and then she told me she can’t because of who he is. Long story short he is someone who works for our brother who is married.
I don’t know his wife super well but I know her a bit. My SIL is pretty good friend with her as well.
I didn’t really dig around about how this happened or anything because I was in shock. I told her she needs to stop this before it’s too late (I actually think it’s already too late if I’m honest) and left. She has tried calling me but I don’t want to talk to her. I wish she had never told me. I also think it’s really fucked up because she seemed almost happy about it? I am really unsure what to do because while I am not friends with this woman, but I feel really bad for her. This is out of character for my sister, so out of character that part of me wondered if she is having some kind of mental health episode? But I think that’s probably just me trying to make excuses for her. I also don’t want my SIL to hate me when/if this all comes out because I really like her.
The only other person I’ve told is my partner, and to be honest I didn’t really want to tell him I just ended up telling him because when I came home he knew something was wrong. He says I should stay out of it and that I should just wash my hands of my sister for a while at least.
I kind of just need to vent because I’m freaking out but if anyone has any advice I would really appreciate it.

There was no need for your partner to answer on your behalf, she's your sister. MM will probably end it now, the thrill of being in an affair fades when the secret is out, he'll probably blame her for telling you. Keep out of this unnecessary drama, you've said your piece. Whatever the outcome you'll probably get the blame anyway.

I don't think that having insecurities is a get out of jail free card for treating others poorly. Just because the sister perceives that the OP was treated better, doesn't mean that she was in reality. I am really sorry for this man's wife: I can't stand this attitude of 'she didn't make promises so it's all the man's fault'. People who have morals don't help others cheat. OP, I wouldn't judge you at all if you wanted to see a lot less of your sister or even cut her off because of this. She sounds like one of those people who blames everyone else for her misfortunes and feels like the world owes her something. I'd be stepping way, way back from this mess, and to be honest I wouldn't help her pick up the pieces, either. She's a grown woman and she needs to do better.

Agree with this except I might not be 'there for her when it falls over'.

Just stay out of it and be thankful that you have never and will never do anything that anyone might judge.

If that's a dig at the OP, it's a very silly one. Of course nobody is perfect, but knowingly having a relationship with a married person is something anyone can avoid. Why are people judging the OP for judging her sister?

Never forget that if she and he can lie to others about something this important they can, and will, lie to you - and about you.

Step back till it's over. And never agree to be part of a slimy secret again. As soon as someone says "Can you keep a secret?" Or "Don't tell anyone but" I say "No, sorry, don't tell me, I'm terrible at keeping secrets and will definitely tell my family. Whatever it is, tell someone else." The only secrets I'll agree to keep are nice surprises and the like.

Liars are dangerous and will happily enmesh you in their grubby shit.

Tell the bloke you know. And tell your brother. Your sister lost all right to privacy when she told you what she was doing with one of your brother’s employees, possibly started via your brother’s business event.

If she was worried about it, it would be different - but saying she’s gleeful - oh dear.

That’s ridiculous. This guy is the OP and her sister’s brother’s employee. He doesn’t get to legislate on his relationships.

I agree to try and keep out of it.

It's very telling that she said she was concerned for you - she's really trying to justify her very wrong relationship by pretending that yours is also wrong.

I would try to put it out of your mind, go on holiday and tell your sister that you don't want to discuss the affair again.

This is waaay too dramatic and all about you.
Not condoning affairs but honestly give your sister a break.

Why should she 'give her sister a break'?! I honestly feel I'm taking crazy pills reading this thread. The sister is the one who is dragging OP into her drama, and then turning around and being manipulative when the OP and her partner set appropriate boundaries.

I agree @Crowgirl

Giving a sister some sort of cold shoulder is going to make her feel so shit. She'll end up clinging to him because her family are cold shouldering her and she's going to feel even more isolated from her family.

Just take the call, tell her she deserves better and that you'll chat when you get home.

Your sister sounds like a self pitying tool. I have one too. Your post touched a nerve - I am just back from a weekend with an elderly aunt who I haven't seen for decades telling me my sister was not favoured like I was by our father. I know all this, I've been hearing it for decades.

What nobody realises is that it's also not brilliant being the favourite if you carry guilt about it your whole adult life. You're not responsible for your parents' failings OP and your sister is a grown woman now, she can get therapy and stop expecting you to make it better for her.

Re the MM; again the type of crap I'd expect from my older sister. She is not single but phoned me all gushing and wanting to share 'the hot sex gossip' about not her partner but her neighbour. She then got all prickly with me because I wasn't appropriately excited. This neighbour had been pursuing her for ages which she found hilarious then when she decided to end things called him a psycho at every available opportunity for not melting away into the background. I know her partner very well and am disgusted. When I asked her if she was breaking up with her partner she yelled at me for being judgmental.

I'm so so so over her selfish melodramatic shit.

Your sister is pathetic calling this man her boyfriend. It's an affair. She should own it at least. As for the faux concern for you... I'd take a massive step back just for this alone.

Finally, a sensible post! I agree with every single word.

She deserves to feel like shit if she is knowingly sleeping with a married man.

This 100%

Your DSis is panicking like mad now, she thought you'd be happy for her, but she'd given no thought to you being unhappy with her behaviour. If you tell on her she can see her new happiness going out the window, so she's probably desperate to talk and be sure you won't tell anyone. Sadly, she probably sees this as a great love, but if the MM's wife gets any idea he's cheating he'll deny everything and drop her like a hot potato. In your place I'd tell her you won't tell anyone but you won't lie for her either, no being used as an excuse so they can see each other

Yep. This.

Oh, and the "I'm worried for you" accusing your partner of being aggressive when he wasn't - that's EXTREMELY concerning. She may be trying to set you both up as unreliable as she realises she should have kept her grubby behaviour to herself and has realised there may be repercussions.

Untrustworthy people are Untrustworthy with everyone. Be careful. The only way to deal with this is to give it absolutely no oxygen.

I thought you meant she was your DH's OW!

OP, you're being a drama queen. This is not about you. STFU, be there for your sister, whom you say you love (even though she was paid to look after you when you were small - why did you tell us that btw?) and deny knowing anything if necessary. Except that you seem to love telling people things they don't need to know.

I was all for it’s not your business, leave her to it until she started saying your dh wasn’t safe.
She couldn’t get you to talk to her, so she showed you she was willing to hurt your husband to get her way.
it was clearly a threat to get you to respond to her and it worked and she’s been reassured.

i don’t think after that treatment of my dh I cba dealing with her at all to be honest. And I would definitely look out for her putting a wedge between you and dh and your brother, to get ahead of any risk of you telling him.

if I were you I’d be torn between not speaking to her for a while or telling everyone everything - DSis is having an affair with x man at DBs work, she told me and then when I was uncomfortable and didn’t want a conversation with her she’s implied that actually my dh is controlling and aggressive and I’m unsafe with him. I am not getting involved with any of that and neither is DH, so now the truth is out and you can do what you want with it.

Stay out of it and think of it as a phase if it helps you get on with your sister better and be there for her when it ends badly. She's responsible for her own choices but she's acting from a bad place. It sounds like she's wanting to be the one 'chosen' by this married man in the way she feels she wasn't by your dad, it's like re-living the competition to try and 'win' this time.

I think it’s nigh on impossible to ‘stay out’ of a situation that you are now actually dragged into, like it or not, purely through her decision to tell you what she is doing.
Affairs are based on secrets and function on a day to day basis by means of lies. You have been dragged into this by her sharing her secret and presuming that you will stay silent, thereby lying for her by omission.
You are now unwillingly complicit in keeping their secret and she is relying on the hope that your relationship with her and with your brother and possibly the MM’s wife will keep you quiet.
It is completely unfair of her to involve you in this way. To gleefully tell you about her relationship with her boyfriend, which in bald reality isn’t Romeo and Juliet, it’s two people colluding in the ongoing deception, gaslighting and abuse of a third, is frankly disgusting and you have every right to express your feelings about that to her without being called judgmental.
Whether you tell anyone involved is entirely up to you, she has willingly involved you and made what once was her business, your business too.

I would tell her exactly how you feel about it, the unfairness of the position she chose to put you in, and tell her to end the relationship before it blows up in her face and she inevitably gets thrown under the bus, when everyone involved will get very badly hurt. You could (if you feel can’t morally withhold information like this which potentially affects others so seriously) tell her that she has to either end it, or tell the MM to come clean and tell his wife, and if they continue to deceive his wife, now with your full knowledge, you will have to seriously consider what you do about it, because you won’t be complicit in the ongoing poor treatment of others like this. You also need to let her know that although you can’t condone her behaviour or help keep her secret, she’s your sister and you will be there for her when the relationship is over.
If I was his wife I’d want to know, so that I had the same choices they make secretly for her every day of their sordid little ‘relationship.’
So sorry she dragged you into this. I would absolutely hate to know that somebody I knew was being duped in this way and I knew about it, but did nothing. When you find out you have been cheated on you wonder who knew, who acted every day as if things were ok, because they thought it was none of their business. I’d wonder why the hell they didn’t tell me and why they were OK with colluding in my deception. It would feel so humiliating knowing they knew but didn’t tell me. If you decide to tell someone then be prepared for the fallout, the truth is often hard to hear. I really feel for you, horrible position to be in. It’s easier to stay out of it and tell yourself it’s their business, not yours. However, she made this your business too OP. You are in it, like it or not.

Well articulated.

I disagree she should confront her sister though. The sister is selfish, entitled and a liar, and hinted at gaslighting with the lie that she was worried about the OP. People like that think nothing of blowing up lives and throwing family under the bus.

We want people to admit reality and be sorry when they're wrong, but most just don't and often liars and cheats escalate to try to salvage the act they want to present to the world.

I think she should avoid her as much as possible for now. Her sister is already telling people so it won't be long before he dumps her.

At least when the wife finds out if she's approached she can show her this thread and prove she was, rightly, disgusted and didn't want to enable the humiliation and abuse of the wife.