Mother In Law Sex

There are many confessions about sex within the family. I thought that I was unusual but it seems not to be so, I have frequent sex with my widowed mother-in-law who is 60, usually at her place but sometimes outside. She's slim and attractive so I wonder why she doesn't find someone. She likes the element of risk, getting caught, so we sometimes drive into the countryside and do it in, or on, the car. Not dogging because there are no others around. I suspect that my wife knows about it because of the jokey comments that she sometimes makes. I say nothing!