Best friend affair

I think its gone way beyond. If her friend had stopped the affair then maybe. The fact the friend is happy to continue the affair.... OP needs to take a big step back!

Distance yourself OP.

I'm sorry but your friend has no moral compass so why do you want to be friends with someone like that? She would fuck your dh without a problem as well, just think about that.

she’s so messed up by it and doesn’t know what she’s doing and what’s going on.

She knows exactly what she's doing and what's going on.

Why ever did she tell you and then expect you to sit over the dinner table from her husband and go on holiday with him.

She's lessened the guilt by sharing it with you.

For me she'd either have to stop the affair and never talk about it again or I would not be in the company of her husband. I couldn't tolerate being complicit in the deceit.

I'd tell her that I don't want to hear any more about it.

Are her husband and your husband friends? How would your husband feel if he found out you knew, lied to his friend or made him have to keep the secret and lie to his friend. This could impact on your marriage if you keep her secret as it looks like you are approving of it (whether or not you do) if you are keeping quiet.

I want to do what’s best for her.
Why for her and not her kids?

You're being pretty damn selfish to be honest. You're prioritising having a friend to socialise with over being a decent human being. You saying she doesn't know why she's doing it and looking for ways to excuse what she's done is absolutely ridiculous.

Cheaters are disgraceful.
People who are covering for cheaters whilst socialising with the person being cheated on, are also bloody awful.

You're obviously such great friends because you both have the same moral compass as eachother.

She's abusing her husband to chase thrills. She's getting a dopamine rush from the risk and secrecy and she's also getting a rush from telling you about it. She's also put you in the middle of it and that's a pretty poor friend in my eyes. She's trying to make you her accessory and she might use you as a front for meeting the other man. I think you'd better let her know that won't happen and you won't cover for her.

She's risking her husband's sexual and reproductive health and the mental and emotional well-being of her family. I see cheating as a form of domestic abuse so
I wouldn't keep her secrets. She'd tell her husband or I would. I'd also end the friendship.

I'm surprised you still call her your best friend OP.

Surely this behaviour and her betrayal of her H and her family must make you see her in a different light? She has revealed herself as deceitful, selfish and totally uncaring about anyone - including you because of the position she has put you in.

Personally i would stop having any contact with her and, if you have any decency, tell her H that she is betraying him and making a fool of him.

Sorry I would have to tell her I can’t socialise with her while she is having this affair due to the horrible position she has put you in. I would tell my husband and if her husband wanted to know why we aren’t meeting up with them then I would refer him to his wife. But then your husband may tell her husband.

I would tell her that it’s only going to end in tears and that she’s not to come running to you when it does that you won’t be there for her

It's unclear what the actual issue is for you. You already know you are not going to tell. If it's just about feeling awkward socialising with both of them, you could try meeting up with just her and skip the dinner parties for a while.

I had this exact scenario around ten years ago. I did exactly what @RapunzelHadExtensions recommended.

She told me and she was part haunted by it but then in he same conversation would go on to tell me how and where they had managed to last meet and how they had nearly got caught.

I told her that I didn’t want to hear about any of the forbidden fruit / exciting/ how great the chemistry is type stuff. However that I would support her to end the affair and would always be a friend of her marriage. I had to regularly see her DH too and he is a lovely guy.
I also strongly suggested she go to therapy which she did and it helped her get to the bottom of it.
Like you I couldn’t bring myself to tell her DH as we were best friends, but I was very honest and firm with her about the likely consequences if she didn’t stop.
It did drag on for a while but I can’t say for sure as she stopped talking to me about most aspects of it.
Her and her DH split up in the end. It wasn’t as a direct result of the affair but they were very different people.
i did find less reasons to actually go to her house as her DH would be there even though he was a friend too.

I am a single parent. At one point we went on holiday with our DCs (this was arrange pre affair) and that was particularly uncomfortable spending so much time with him.
We are still good friends but something shifted in that time ie my absolute trust and respect in her but the guilt was affecting her mental health and I didn’t want to leave her high and dry either.
It’s a very difficult situation OP. I would be quite tough but supportive.

This happened to me. Ultimately our friendship didn't survive as I realised she wasn't who I thought she was. Our morals didn't align and I couldn't continue a friendship with someone so devious & selfish. It was devastating. It did take me several years to come to terms with the loss of her in my life, but also in how wrong I had been about her. I haven't had a close friendship since because if I got her so very wrong for so many years I don't really trust my judgment.

I would just get her to imagine her husband finding out, the look on his face and how she would feel about him feeling the hurt that she has caused him. Also to imagine him leaving her. Explain to her that affairs have a way of coming out as people become complacent. She may consider ending it if the reality of what she's putting at risk.

This would be friendship ending for me. She can stop, she just doesn’t want to because she’s selfish. And now she’s burdened you with the knowledge of her disgusting behaviour, because she’s selfish. If you don’t want to tell her husband, that’s your choice but I’d want nothing more to do with her. She’s put you in a horrible position.

I’d keep it zipped but I wouldn’t socialise with them as a couple

She says she can’t stop it? Of course she could. She just doesn’t want to.
I echo those who have said you need to tell her you don’t want to hear about it any more. Yes, she’s a dear friend but she has put you in an insidious position.

When does she get time to sleep with him multiple times with four children under ten! Is this real?

I’d tell her I don’t want to hear about it but leave it at that
I don’t take up for men over women so it’d not involve myself, and just avoid her husband forevermore

I was wondering how she finds the time!

I imagine her husband must suspect something as she must have a very intense schedules with not a lot of give so if she’s working late a lot more for eg I’m sure he has wondered

how would her life look if he asked for a divorce?

If your DH was having an affair would you want to know?

I couldn't remain friends with someone ike that & I would tell their partner.

If my partner cheated, I would want to know.

You tell her that she needs to tell her husband or you will.

And you end your friendship because if her husband can’t trust her what makes you think you can trust her 🤷‍♀️