Decorating Permitted Sex.

Went round to my mother in laws house eight weeks ago to decorate her lounge.
My wife was working nights at a care home, so I worked late to try and finish the decorating.
My mother in law Jenny, who's fifty one made me a drink and then said she was taking a shower.
About ten minutes later I heard Jenny shouting me to help her.
I ran up stairs to discover my mother in law lay naked on her bed, calling my name and playing with her pussy.
I already knew Jenny, who's good looking and still fit at fifty one, fancied me. Also her daughter would often throw out comments about her mum needing a man like me.
It took me all of a couple of seconds to decide I was going to fuck her.
Getting in between her legs after I dragged my trousers and boxers off, I drove my erect cock straight into her soaking wet c**t. And boy did she want fucking.
It was like two teenagers going at it before I shot my wad after only ten minutes, up her creamy c**t. But Jenny wasn't finished with me, even though she'd orgasmed twice, making me go down on her to lick and suck on her clit.
She came twice more and I got to taste my own cum too.
After she'd settled down from her last orgasm, she told me she'd wanted me to fuck her ever since she saw me screwing her daughter on their living room couch.
I didn't even know she'd seen us, but apparent her daughters had, but had never said anything.
Texting my wife as Jenny put on some clothes, I let her know I might be staying over at her mums overnight, to get the decorating done. My wifes response twenty minutes later was "I'll pick you up in the morning". Then a few seconds later this arrived and i still have it "Mum likes you know. Make her happy. Love you x".
I did stay. Jenny and I fucked all night, then again just before her daughter came to pick me up the following morning.
My wife knew we'd been fucking because the house smelled of sex. Plus I heard them talking in the kitchen with my mother in law telling her daughter, I was really good with my tongue.
My wife didn't mention anything to me on our drive home, but she did make me go down on her when we got in.
All she said was "Mum's right".
Now just over two months on, I've fucked Jenny on lots of occasions, sometimes staying over when my wife works her night shifts. She knows full well I'm fucking her mum, but seems perfectly happy for me to do so.