Before my sister started dating my best friend (since childhood) I used to have sex with her. We really were good in bed together but since she started dating him and they decided to live together we completely stopped. I didn't want to cheat on my best friend. A few months ago I guess my sister told him, of he found out I don't know, he invited me to their place and my sister told me he knew about us having sex before and they would like me to join them in a threesome. Wow!! That was amazing and the truth was that I already missed my sister's pussy a lot.