From my initial suggestion that I'd be okay about it if she had sex with someone else to her actually doing it was over 2 years. Her first reaction was "Yeah, as if!", but slowly but surely she realised that I was actually serious. We sometimes talk about possible scenarios in bed, usually after she had a dr1nk or two, but the introduction of a realistic looking sex toy (bought for her as a joke as a present by neighbours returning from holiday) into our foreplay definitely pushed things along.
Using it on my wife in bed really aroused me as I told her how good it was watching "another man's cock" going in and out of her and how naughty she was doing it with "him" right there in front of her husband. This turned her on as she came stronger and noisier than usual, murmuring, "Yeah, and you love it!"
Ground rules were agreed. Despite the fact that she'd been sterilised we felt it a good idea that she use condoms that I would buy for her and that she wouldn't go with anyone I knew so I couldn't put a face to the name. Later I readily accepted both rules going by the board as an ex-workmate of mine, after years of trying, succeeded at last in getting my wife into bed and pumping a copious amount of cum into her. Her pussy, her rules I suppose.
The first extra-marital coupling I was fully aware of was with a customer at the shop she worked in. He was only 23 but asked my wife out for a dr1nk, unperturbed by the knowledge that she was just about to turn 35 and married with 4 kids. This came as a bit of a surprise as we'd fully expected one of her delivery lorry drivers who'd also been chatting her up to be first, but this young lad beat him to that married pussy.
Peter C