"Man enjoys MFF threesome" might be the least shocking headline since "Woman cold".
That's always been a big fear of mine too, "Who catches feelings". I've heard of far, far more breakups from threesomes than surviving relationships. In fact, there's a well known story amongst my wife's friend group involving one of their parents. The dad is very, very, very flirtatious to the point where he hits on his daughter's friends, which is gross. He and his wife have been married a long time, but she's clearly miserable while he's openly trolling for ass. At a wedding, she got a bit tipsy and told the friend group, "Never invite someone else into your bedroom. It ruins your marriage."
I think that's great advice, however I also know it doesn't apply to everyone. As Nina Hartley said of the porn industry and I'm paraphrasing, "It's not for everyone. Sure anyone can do it, but most people cannot handle it."
In the example I gave, the husband is clearly immature in that aspect of life, and thus, was not a good partner for a threesome. You and your wife definitely seem to have done it correctly. This wasn't out of the blue. This was years of discussing it with one another, you bringing it up here, testing the waters over and over, and so on. Just stay that same course, and you'll probably get more. Definitely don't start asking your wife daily when you get to do it again!

Genuinely good on you for offering, and your wife's answer makes perfect sense.
Tried this once on a drunken evening three decades ago (fuck I'm old) and it wasn't for me. Sorry to burst Cake's fantasy bubble, but the guy and I were never within her body length of one another. This is going to sound odd from someone with my past, but it was a turn off for me because it reduced her in the moment to just a tool...if that makes sense. Even though I enjoyed my MFF adventures when I was a young single man, I prefer the 1 on 1 situation.