It wasn't planned it just started

In May of 2023, my sister 26 got pregnant and her boyfriend left her to raise the child alone. Our father had deserted us years earlier and our mother passed away due to cancer in 2020. I (30) had a great job and was paying off my own home, my sister came to live with me after her now ex-boyfriend left. I've never been great with women, had some minor successes over the years nothing lasted. Anyway, early morning of July fourth, 2023, we were both home nothing planned. My sister still in her revealing PJ's bent over in front of me and I got an instant hard-on. I also was in my PJ's and my cock poked out of the fly. Before I could adjust myself, my sister turned saw my erection and had a giggle. But then she went quiet and still looking at my hard cock. She then shocked me by straight out asking me to fuck her, adding I can't get more pregnant than I'm already. Aroused I agreed and we started having regular sex. When her daughter arrived, I assumed the sex would stop. But it had become a normal part of our relationship by then and she still slept with me every night. Regular sex continued as before, after she weened her daughter, she didn't take any precautions. Neither did I, I didn't even think about precautions. As a result, my sister is now pregnant to me all tests show no problems. I'm quite happy with our relationship as is she.