My neighbor cheated with his partner's sister, and now lives with the sister. The most aggravating part of it is that he has kids with both. Every other week his ex has to come by to drop off her kids at her sister's house since they share custody. From the kids perspective, their sibling is also their cousin.
From the kids perspective, their sibling is also their cousin.
I have a genetic half brother in my mom's side. But since he's older than me, my biological father adopted him, and he has literally always lived with only us, I just view him simply as my brother. I always have.
My mom has an identical twin. Her twin's children - my cousins - are genetically just as related to me as my half brother, who I view simply as my brother.
The one that we made a sexy time video years ago that I have since forgotten that it was still in on my computer, that she found and it caused a big argument.
When both people in a relationship are in the leadership of an organization, it's a serious problem when one of them cheats with someone else also in the leadership of that organization. A friend of mine was part of an organization where this happened, the drama was terrible.
My husband’s ex-wife cheated on him with his brother and best friend. It would be completely terrible to cheat with those people even without that history, but it makes it 10x worse.
Someone else that they trust a lot that they introduced you to to help you out of a jam.
I've seen the best friends one a couple of times and it completely destroys the dynamic obviously. One guy isolated himself and spent a year drunk and on /pol/ and the first conversation I had with him after that was about how the holocaust didn't happen. Idek if cheating happened in that instance or if she just lined up his best friend really quickly.
Everyone new I meet seems to be polyamorous now but I just hear about less relationship drama generally.
There's only one right answer to this question and it's the one person that will make him/her feel stupid for trusting you, AKA "the friend you told them not to worry about"
They'd have a hard time believing it if I cheated on them with my partner. It's so diabolical and unexpected that they'll never convince anybody I cheated on them with themself!