To tell woman about her partner's kinks?

This

This... talk to him.

an acquaintance told me about an ex cheating on me. She was his friend, not mine at the time. Thought it was odd when she asked me out for a drink but she seemed nice so I said yes.

Despite it being so hard to hear, I am forever grateful for her sticking her beak in. Me and her remained good friends for some time. Him and her fought about her telling me and never spoke again.

I was in a committed relationship with this guy . I’m not sure how your friend and the pregnant lady are together if they are in a situationship, or if that’s his words rather than hers!

If I were the one with your friend, I’d appreciate someone sticking their beak in for me. But just be prepared it would most likely be the end of the friendship.

If they're actually in a relationship, I'd tell her. The friendship is ruined because of this anyway, and if she's sleeping with him (especially while pregnant) she needs to know that he's cheating on her with so many people.

I can’t believe the defenders of liberty on here who think it’s ok to keep a woman in the dark about her partner’s dangerous behaviour.

She’s unexpectedly pregnant by a man who shags around- regardless of the name- and she needs to know for her heath and the baby’s.

Poor Woman. But no, keep her in the dark, or you’ll be interfering.

I can’t believe the abuse you’re getting here, OP.
You need to labour the point that she needs to know because it affects the health of his unborn baby. This could be life threatening.

It’s not that she thinks she knows best, but that she thinks the other woman has a right to know. The woman is running a risk if she’s sleeping with a man who is sleeping with many other women, and I think she has a right to know she’s running that risk.

If I was that woman I’d want to know. And I’d be furious if I discovered that someone knew about it, and could have told me but didn’t.

This is a good compromise. If he really won’t tell her, even with a great deal of urging and reasoning for the health of the baby.

If he’s had unprotected sex with a woman who he’s not in a committed relationship with, and who doesn’t even live in the same country, when he’s that high risk for STIs, then it’s very likely he’s generally cavalier with protection, thus making him even higher risk.

Hmm, tough one. If he’s a very long-standing friend, it’d be disrespectful to him to tell her behind his back. So, it would probably end your friendship.

However, if you’ve urged him to be honest with her and he won’t, and you feel this has already ruined your friendship, then maybe you have little to lose?

I’d keep urging him to tell her himself. What’s his reason for not telling her? Does he say it’s because he plans to stop the swinging? Roughly how old is he? If he’s now older, maybe becoming a father will mean he changes his ways. Also, how far pregnant is she? Too late for an abortion?

If the child is definitely going to be born, s/he should have as much chance as possible to have parents who are together or at least get on well. Telling the mother could jeopardise that and make life harder for the child before it’s even born.

Then again having a child with, and maybe occasionally having sex with, a man who isn’t honest with her and regularly has sex with strangers, could put her emotionally or physically at risk.

And potentially risking her and her unborn child's life with regards to STDs. Yes I know they test you for HIV and Syphilis and something else that I can't remember, but if he's shagging around and having sex with his partner it still puts her at risk.

I can't imagine approaching a 'distant aquaintance' about her 'situationship'. You seem itching to create drama!

So he’s in his 50s at least (calculating by 30+ years friendship) and she’s late 30s at most (to still get pregnant easily). Is there a power imbalance, is she so naive and doesn’t know what’s going on? I’d like to think I’d tell her for the sake of her health but I don’t know if I’d be brave enough if I didn’t know her well.

I'm in the "I'd want to know" camp. Also don't get the "are you jealous" comments - says more about the posters than the OP imo. Never heard of looking out for each other? That's exactly how cheats keep cheating.
You're either keeping his secrets for him or you're not - would be better for you if you didn't know about it in the first place but he's clearly told you all this so now you have to choose what you do with this info. After decades of friendship surely he'd know you well enough to expect you to tell her anyway?

Tell her please. How far advanced is her pregnancy? I know I wouldn't want a child with someone like him, she probably became pregnant by accident and is currently trying to make the best of things but if the pregnancy is still early, she has choices. I don't often say that and at first wondered about your motives but as I read on, saw that you had told him to tell her and that your friendship is now spoiled, I believe you are not involved with him and just want to do the right thing.

If she knows the score she can make an informed decision. Don't delay!

If he is in a physical relationship with her and actively cheating on her then yes, I think she deserves to know. Quite aside from anything else he is putting the health of her and her unborn baby at risk without informing her.
Calling it swinging is a smokescreen imo. He is cheating with multiple other people . Why is irrelevant, he hasn't given her the opportunity to make an informed decision.

it's really not any of my business and I should probably leave it well alone.

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No of course don't tell her. It's so far from being your business it's in the stratosphere.

I would let her know he’s a swinger and to test for STI’s to protect her unborn child.

She said they already have fallen out over it.

He won’t be your friend for much longer if you do tell her. If you are so disgusted at your friends behaviour that you want to tell this woman, why is he even your friend? It’s certainly one way to end a friendship.

She might be into it too.

I would inform her that, in consideration of her unborn child, there is good reason to ask her doctor to screen her for STIs.
I would tell your male friend that you have told her.

I would then leave well alone.

I agree.

This is just another version of the old-age dilemma "my-friend's-husband-is-cheating-shall-I-tell-her?"

You're "damned if you do and damned if you don't".

Personally I'd stay out of it and limit your contact with this person.

Well sooner or later, she'll find out what he's into and at that point it will be up to her what happens now.

I don't think you should get involved. Just because he's into group sex that doesn't make him a bad person, or a criminal.

That's what I'm wondering !