Recommended reading: https://www.reddit.com/r/gonewildstories/comments/3nzo8u/mff_wife_surprised_me_in_vegas_with_a_threesome/
Back in September I had to go to Vegas for a conference. My wife, Amy, and one of our closest friends, Carrie, flew out to spend the weekend after the conference with me. Carrie was dealing with the end of a relationship, and, very long story short, her and my wife got all kinds of freaky with each other while I watched (and eventually fucked my wife). My wife kind of orchestrated the whole thing, she's awesome that way.
Well, since that weekend, a fair amount has happened. Carrie stayed with us until she started a new lease in November. She was clearly working through some stuff. I travel a lot for work, and wasn't home much until recently. Admitting I wanted to fuck Carrie kind of came back to haunt me though, because my wife insisted on keeping me up to date on all the sex-related events happening. She and Carrie didn't anything together, sexually, but they did go shopping a fair amount, and my wife told me that Carrie has been buying all kinds of sexy stuff, skirts, tops, new underwear, etc… Apparently Carrie was hooking up a few times a week, and had started using Tinder with regularity. Amy actually recorded one of Carrie's sessions and made sure to play it for me on one of our FaceTimes. Weirdest boner I've had in a while.