I've known Ste my neighbour for nearly 20 years. Both being married we would often visit each others houses for drinks as couples or, if the girls went out we'd have a lads night in, gaming and chatting "boy" stuff. We both work shifts for different companies and now and again we would find ourselves both on nights and chatting online.
Sex had never really popped up in the conversation, possibly once or twice we'd share a favorite bit of porn but it was very rare. One night we were both on nights, chatting as usual when we started discussing posts and groups on a certain social media site. I was fairly new to it so was unaware there was an adult side of things waiting to be explored. He must have shared a post which opened a rabbit hole of new discoveries. We were soon exchanging links to things we liked and started discussing what turns us on. All still very mild but this continued over the course of a couple of shifts, each time the rabbit hole getting a little deeper and the fetishes/fantasies a little darker.
I can't remember when exactly I confessed I'd often fantasied about the two of us having a threesome with my wife but Ste was definitely shocked when I told him. I explained mmf porn had always been a favourite and it was easy to imagine it happening with him and my wife when she came home drunk from a girls night out. We went on to discuss things in more and more detail and he admitted he'd always had the hots for her. I would try to describe how she looked naked and what we were both into sex wise.