Wife is invited into bisexuality by a mutual friend

I'm a guy who has been married for a long time to a very lovely woman. Unfortunately, as I assume with many couples, our sex life went from weekly to monthly to annually. We are committed to one another in many ways, but that reality was a sad one. I'm highly sexual, but my wife has never been.

Over the years my wife has made overtly sexual comments about actresses and women she sees when we've been out and about. At first I made nothing of it, because women talk. A lot. Then I realized that maybe my wife was bisexual after all. She'd always denied it, but her comments about other women definitely piqued my curiosity.

About a month ago one of our female friends from our group of male and female friends (singles, couples, LGBT+, etc) asked me candidly if my wife was bisexual -- as we stood outside smoking. I denied it, lying, claiming that I had never observed any such thing. She basically said that she was interested in being with my wife, and hoped that I wouldn't be offended that she just said so.

I took a long drag from my cigarette, and flatly told her that I was fine if she tried to seduce my wife. But there would be conditions. The first condition was that I wouldn't be around, probably when I was traveling for work. The second condition was that she told me everything about their time together, even if my wife didn't. The third condition was that she and I would have our own try (I found her quite attractive in completely different ways than my own wife).

A few weeks after our chat I had to travel for business. As people in our group of friends would regularly send innocuous text messages, I simply texted her asking if she'd check in on my wife while I was out of town. She replied with some emoji, and I went on my business trip like I normally do. I couldn't focus, and I couldn't wait to get home. I wondered if our friend would follow through with what she'd asked of me.

When I got home my wife had a spring in her step like I had not seen before. I played coy and asked her if she'd gotten a promotion at work, or a raise. My wife demurred about whatever had taken place. She didn't seem to feel guilt or shame. She just wasn't telling me the truth, and I knew it.

Conveniently, my wife decided to fly out and visit her family. I texted our friend, and she knew my wife was away. She asked me to come over, if I'd like, for dinner and drinks.

At first everything was normal. We ate, drank, had a few laughs, you know, just like we always did. Our friend, usually a tomboy, was dressed quite nicely. I enjoyed her short skirt, her heels, and how she was showing a lot of cleavage. After dinner she said plainly that it was time to go to her room. As we enjoyed some sexual time, she talked to me, and divulged thrilling after thrilling moment of how she'd seduced my wife, or rather how my wife had seduced her.