I loved my wife having an MFM. I wasn't a cuck in that I'd let anyone humiliate me, handle his dick, etc.
I'd help my wife set up her date, shaving her legs, picking out the outfit, etc. We'd usually meet the guy in a bar and if she wanted to bring him home while they were getting comfortable with each other I'd get them a drink, set up the bedroom with candles and music. Then I'd observe for awhile, taking pictures if the guy didn't object. I enjoyed watching the seduction, the first contacts, and then them making love.
When he was beginning to run out of steam, I'd join them on the bed, screwing my wife while he watched and helped. Usually, that led to more sexy thoughts on his part, which led to more sex between them.
We were very comfortable with that scenario. Perhaps that could be your niche.