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.