My sister in law was so desperate for a child it was at the point of ruining their marriage she confessed to me and i jokingly said take one of our four. It was a drunken remark and seeing her tears flow i gave her a cuddle and apologized for being so insensitive. My wife tore into me and my brother looked at me with hatred in his eyes. I took a call from my sister in law a few days later to meet her at my brothers house and on arrival i began apologizing again. She asked if id consider fathering a child with her but keeping it to ourselves. Id put my sperm into a syringe and she would then use it hoping to get pregnant. I agreed and after quite a few attempts it wasn’t working. She told me to go round to hers that evening to try again but as i walked in she was naked under an almost see through nightie. Lets try another way she said leading me upstairs. We made love and god the sex was incredible. I cum in her twice with her laying on the floor her pussy in the air and me stooping over her. It took just three attempts and she successfully became pregnant giving birth to a beautiful boy. After about six months i asked is everything ok now and she kissed me thanking me telling me i was a far better lover than my brother and she never orgasmed with him like she had with me. I confessed sex with her was hotter than with my wife and we began meeting again and fucking her was all i could think about. She got pregnant again and has a daughter too now. Our secret stays safe and we still fuck but far fewer times now.