The thing that gets me about all this wife / husband / belonging lark is...
Whats the problem? Its just a 'bunk up'
I think it is the people who obsess over fidelity who have the problem.
The way I see it is that you want to know your kids are your own, for the sake of Darwin, and that's it.
A relationship is kept for the sake of the children and you do what you have to in order that everyone benefits.
What difference does it make if a partner does it with someone else? Is it like a car and you don't want anyone else sitting in it?
If its because you are worried he / she will run off then its understandable, but if you can't put it into words, just feel angry when someone even looks at your partner, then you have internal issues.
As for you DJ, you can easily neutralize it at your age, since you have only started having these thoughts recently. But if you are not planning any more children, why not indulge?
What do you think 'personal trainers' are for? Pick her a nice young athletic pretty boy. Keep it a secret between you and him, everyone has loads of fun. The spice will be back in your life and the sparkle in her eye.
You can also keep the video evidence to stop the ear assault when she catches you with next doors wife.