After years away she returned

My sister went away after university and was gone 9 years and she returned last November and came to stay with me. I'm her only sibling and the younger by 3 years, I have my own business and a failed marriage behind me. I have a son 4 who my ex decided reminded her of me and so left him with me with me to live her life to the fullest. That didn't go well for her, as the new man in her life. Got drugged up and took her life as a result, so I run my business and care for my son. On the return of my sister, there wasn't anything special going on in my life and I continued on as before. My sister got herself a job and in February she joined me in my bed one night and got me to fuck her. Which I did and she started to sleep with me every night since. In May she asked me to get her pregnant and I agreed, I got her pregnant by July and every test says the child is healthy. I hadn't been dating as I had a business to tun and my son to take care of and my sister joining me in my bed was a benefit for us both.