Wife and I have always been open to the idea, tried it a few times, all positive experiences, even the challenging ones. We dated this single female friend together for a while, we’ve gone to sex clubs (there’s a great, super positive one in my city). I feel like it’s made us more honest and open with each other.
If I could recommend a book, “The ethical slut” There’s good tips and info in there, I liked it, though it’s a bit old. “More than two” is newer and great as well