After I met my current wife, she was such a sexual monster I thought she might 'play' with others, perhaps get involved in 'the swinging lifestyle', but I was mistaken. I didin't come right out front and center about it, and I'm glad I didn't...given her reaction...because it may have soured our relationship, that later turned into a marriage.
If your fantasy developed by watching cuck behavior on porn sites, keep in mind these people are actors. It would take a special mindset for 'real' people to proceed with it. Way way back I was involved in a couple events like this, and the anticipation was more enjoyable than the actual act. Once everyone had their orgasms, things got really weird.
Tread lightly, for once that question is asked it can never be taken back.