Swapped by birth: 70s, threesome

 It's year 1975. 
A new era. Looking at us, it's hard to believe that just a year ago we were Brett, Vernon, and Arlene. Now we're Betty, Veronica, and Arnold. We'd been friends since childhood, going on trips together, even to Woodstock. So it turned out we were actually swapped by birth, all three of us, who would have thought? When we received the notification from the original owners, we assumed it was the universe telling us our souls were in the wrong place, so we agreed without hesitation. After the procedure, we felt a strange dissonance; on the one hand, we felt the differences in our bodies, and on the other, we felt whole for the first time. Betty, especially, who had the most resistance, embraced her feminine nature the most.  Two months after returning to our true selves, Arnold suggested changing our dynamic, letting us not just be friends but more, threesome concubinage. It was something she'd considered before the discovery, but she hadn't thought we'd go through with it. Yes, we had sex before the swap (and afterward, too), but we saw it as friends with benefits with no strings attached, so it was all the more surprising that all of us had considered concubinage but hadn't thought others would agree to it. Another sign from the universe that the swap was the right one. And so, a year later, we're all living happily together, just as it was meant to be from the start.