The thing that I see here is that you were blindsided -- you didn't guess that your wife might sleep with this guy so soon. If she had come back from the date and said "Hey, I like this guy and I think I might want to get physical with him, what do you think?" you could have had time to process the idea and get used to it and maybe say "How about no sex until I meet him" or whatever you may have needed to be comfortable. It may be that just her telling you first would have been enough to achieve that. But nobody likes to be surprised by something hard.
Next time, you guys will know better and can communicate more. In poly, I find it's a good practice to discuss ANY new step before it's taken.
The major players. Me, under-30 bi female. Gia, girlfriend of 3+ years. Clay, new boyfriend/dom. Davis, ex/"it's complicated."
The supporting cast. Eric, Gia's husband. Bee, Gia and Eric's toddler. Dexter, Gia's lover. Helen, Eric's lover. Izzy and Nikki, Clay's partners. June and Royce, Izzy's partners.