My wife's girlfriend was sleeping with us, and she took my cock anal a few times while my wife watched. In their private time together, she advised my wife to try it. She assured her I was a good ass fuck. The following year she decided to try it during her summer break. I tried to be easy with her. We spent a few weeks licking, fingering, and toying it before I put my cock in. The first time made her sore. But after a week, we did it again. After a few times, she wasn't sore from it and she eventually started asking me for it a few times per month.
