Comforting My Mother

Short History. I'm now 35 and my mother was 15 when she had me and married my father then 24. Anyway, fast forward 19 years and my father died in a motorcycle accident, my mother was shattered. I was working as a mechanic having left school at 15 to train as a mechanic. I was still living at home with my mother 35 and sister 17, we were okay financially as we own our home, and all had good jobs. Neither me nor my sister could be called scholars and we had left school to train in a trade rather than waste our time failing at school. My sister was a trainee hairdresser and my mother worked at the local library. My father was also a mechanic and liked fast motorbikes and his first major accident was his last. I dated and like being at school failed, but still kept trying. After several months, my mother and I were home on a Saturday, and she was feeling low, and my sister was working doing a wedding party. It was overcast and a I decided to comfort my mother, I gave her a cuddle and one thing led to another and we ended up in her bed fucking. She took my virginity that day and as they say once you start it's hard to stop. No worrying about her getting pregnant as she had trouble with sister birth and after an operation that followed couldn't have any more children. It was a perfect arrangement, and we continued our sexual relationship and would include my sister when caught us in the act 4 years later. She of course could've children and I found that out the hard way with her getting pregnant to me. After tests showed no problems, we moved interstate to start anew. With my sister acting as my wife and our mother still sleeping with both of us, we were and are very happy with like style. Now have 4 children and all are healthy, our mother hurt herself in a fall and now needs a walking stick to get around. She stopped working and became the Childrens fulltime carer. She takes them to school and picks them up afterwards and is with them when my sister and I are working. She also is in charge of the house and it's her house and children ask her for things they want, like getting a dog. She still likes having sex and provides most of my sex as my sister is tired after work and only provide me sex on weekends, but my mother will anytime I ask.