Now it was Cassie’s turn. Kneeling between my legs she deftly threaded one ball through a metal ring, and then the other. She began to kiss and suck...my flaccid cock, and I started to stiffen immediately. When I was still only partially erect, she fed my cock through a second metal ring, which was attached to the first by a short leather strap. Cassie then took my cock completely in her mouth and began to suck, gently at first, but then more fiercely. My cock quickly hardened and grew, the cock. We’d fuck quietly and then she’d return to him. She knew that I could always hear Doug’s bed thumping when they fucked and would stroke my own erection in synchrony, although I saved the ejaculations for the mornings.Then came a watershed event. Doug’s company sent him on a two-week field assignment. He’d not said anything about the growing familiarity between GF and me but did say, “Take good care of her” as he left.It was wonderful to have her all to myself on those visits. We talked a lot. The shade beneath the canopy felt wonderful after the hike in the hot June sun - and the best was yet to come.There was work to do first, though.He pulled his arms out of the straps of his backpack and retrieved a water bottle from the side pocket. Thirst quenched, he sat down and leaned against the trunk of a large maple. Pushing aside the trash bags he was glad he hadn't needed, he pulled his laptop from the backpack and inserted the first flash card.As expected, most of the images were of. Suddenly I felt Kamy squeeze her thighs together and she made contact with my naked cock for the fisrt time. I was horrified thinking that she would freak. She looked at me with what seemed like a shock expression. She didn't relieve my cock form the grip her thighs had on it though, and that could only be a good thing. Meanwhile my sisters panty kept riding into the slit of her moist pussy, which soon became transparent due to her copious amounts of puss juice. Her neatly trimmed landing.