Desperate Sister

Never on good terms with my younger sister growing up, I went to university graduated and started a great job. My sister married (18) instead having got pregnant and having a daughter. Her marriage wasn't very good, and he finally divorced and also claimed the daughter wasn't his but refuse DNA testing. He also left before the divorce case was finished and disappeared overseas. My sister worked low paid jobs to get by and support her daughter, our parents had already passed away from heart attack (father) and cancer (mother) our brother the middle child died on active service and so it was only me left. I then 40 single and had my own home and able to work from home if needed. My sister 35 at the time was really desperate, because she contacted me. She needed help and I was all there was, I decided to help her mainly because of my niece then 17. I paid for their travel to live with me that was just before Christmas 2019. My sister started to look for work and found only low paid jobs available. My niece was in school and was doing very well but wasn't thinking of university because of the cost. I told her I would pay her way, if she done well and in top 5 of her year, she would get 4th and I would honor my promise. Of course, the pandemic and the lockdown started and the 3 of us were in the house 24/7. My niece studied hard to keep up with everything, I worked from home and had video meetings. My sister started to climb the walls you could say as she hadn't anything to keep her active. Reading books or watching TV didn't help all that much either. But by pure chance she came into my bathroom to get my washing, albeit at 8pm, she was going wash just for something to do. I was in the bathroom and was stroking my cock and got caught by my sister who just entered. After an awkward moment or two, she asked me straight if I would like her to help me. I had dated and never found my ideal woman. I also used hookers at times and my sister offering to stroke my cock was a bit out there, but I accepted anyway. My sister suggested we go to my bed, and we did, she also undressed and started stroking my cock again, then she started to suck it and finally mounted me. I thought she knew what she was doing and never asked if she was protected. Turns out she wasn't she just wanted sex and she didn't think it thru, I'd gave a second or 2 thought, but she thought had it covered and went with the flow you could say. But I admit I was happy getting fucked and would've continued even if she told me she was unprotected. Long story she got pregnant as result, our baby boy born in 2021. My niece was happy to have a baby brother and still happy her mother is having another girl soon to me as we haven't stopped our sexual relationship since that first time my sister act as my wife and change back to her maiden name. The only real change is my niece going to the local university and has decided to join her mother and fuck me. Which is great as my sister has stopped sex until after the birth of our daughter. My niece takes precautions and is unlikely to get pregnant unless she decides too.