Sperm Doner To Sister In Law

A few years ago now. I got my sister-in-law pregnant but it was consensual. It turned out that her husband had a low sperm count so conception was unlikely. It was sister-in-law that approached my wife to ask me to do the deed. I thought that it was a trap so refused but several requests later I agreed. My wife and her sister agreed on a time for best fertility and she came to our house. It was strange having sex with her knowing that my wife was downstairs. The rules were that it was quick, plain missionary sex and I had to cum as soon as possible, no trying to get more. We did it every afternoon for a week. The really strange thing was that after each session, my wife and her sister would sit and chat as if nothing had happened.