My Mother-in-law (Mil)

My Mil (widow) was snobbish with didn't concern me all that much as she ignored me most of the time. But her social position was her whole life, she rarely drank, and I found out why. Alcohol affected her quickly, very quickly and she didn't want that at any cost. At parties she had a glass of wine and carried almost all the party. Sneaking nonalcoholic drinks now and then. That led to her drinking nonalcoholic punch, it should've been the safe opposition. But the children had gone off to play overside and so someone added alcohol to the punch. My Mil drank it a couple of times at least and she was soon affected. Lucky for her I was at the party, my pregnant wife had work interstate and so she wasn't there. I was there because I'd to show up and so arrived late planned to walk around saying hello and leaving as soon as I could. That changed when I came across my Mil sitting in a corner, happily unnoticed at the time. I realized she wasn't well, I didn't know she was drunk at that moment. Seizing my chance, I told the hostess my Mil was ill, and I would take her to her doctor. Taking her to my car I then realized she was drunk. So, I took her to my apartment, it's in the same building as hers. All the doors have pin codes, and I don't know hers. My wife does but she would be asleep I thought and we've a spare bed. Giving her coffee at the apartment, she slowly sobered up, I put her on the bed with a blanket over her. Said I'll see her in the morning and went to my room. Around 6am she joined me in my bed, after alcohol she got very horny I found out. Especially that time as it had been several years since her last fuck. Wanting sex with me to keep it in the family, I got aroused myself and so I fucked her twice. Later on, I drove over to pick up her car and she saw the hostess. Said she had reaction to needle she'd gotten for her upcoming trip, which she might now cancel as she had to have another booster. Back at the apartment building I was sitting thinking over my fucking my Mil and got another hard-on. It was then my doorbell rang, it was Mil she was again horny and so we fucked again. She became a regular fuck for me. Especially when my wife stopped sex before the birth of son. My crafty Mil saw it as an opportunity, talking to her daughter about her our lack of sex. Saying how her late father had only played up on her during the later stages of her pregnancy. Suggested a solution of satisfying herself and keeping in the family, my wife trusted her mother totally and agreed to ask me to fuck her mother. I was suitable shocked, as I hadn't been told about it prior and so I reluctantly agreed. No sneaking around anymore, my Mil sharing our bed and still seeing me alone as well. It didn't stop once my wife was back having sex with me, her mother joined in threesomes. When we moved to our house due to another child arriving soon, her mother moved in with us and is still with us today and we now have 4 children.