What an interesting Friday the 13. I let my 17 old son stay home today and thought nothing of it. I was suppose to be at work till 6 or 7 this evening but things went exceptionally well and I was off by noon. As such I proceed home to sit in my hot tub and drink jack. When I arrived my sons girlfriends of 2yrs car was parked in the drive. Taken no mind to it I walked in and the house was a ghost town. I thought they may already be in the pool or the hot tub I headed up stairs to change. After making it to the top I heard an unusual set of sounds, it sounds like hitting your fist in your hand and a mix of male and female moaning. My sons door was cracked and I smiled in a proud father stature thinking I was about to get a glimpse of my son fucking his gf "finally, good for him" I thought. Yeah, not how it went down. As I peered into the room my son was laid flat down on his stomach, dick between his legs and his girlfriend was wearing a large strap on and stroking in and out of him. *shocker*
I was in shock and awe and wanted to say something or walk away but I walked as she owned his ass and in doing so have me the erection of an eighteen year old. I watch this girl drill his ass to the point of making him cum, where I about lost it was when she look at me through the crack and with her tongue out, winked at me. Quickly leaving the scene, I changed, grabbed my jack and headed to the hot tub. I tried not to think of it, or question if she saw me or not but the whole situation running through my mind kept bring back my hard on.
Moments after I begun my drink my sons girl came out in minimal clothing, smiling, and leaned over to talk to me showing her cleavage. I was so proud of my son for scoring such a sweet sexy fox college girl. She started to tell me that she knew I was there, that I watched the whole thing and knew I was arroused, of course I denied. She stopped me and said, do you know why I fuck your son in the ass? Silence... Because his kinky fantasy is his father taking him up the ass with your big cock that he's seen and you filling up and telling him that you love him. With that she was off leaving me speechless.
In an instant I took my shorts off sitting in the tub stroking myself and sipping jack. I heard her car start and drive off. Not to long later my son came and sat with me not noticing I was in the nude *awkward* he acted like nothing had happened. I struck up some basic conversation and we talked for a good 20 or so minutes before I decided to get another drink. My son noticing I didn't have a ice ball in my glass offered to retrieve me one which worked out well as I needed to get my shorts from the backside of the hot tub. As he went in I tried leaning over bit to no avail. I had to jump out and just as I went to put them back out my son walked out catching me nude looking like i was getting naked. His quick response was only to join me naked as well and I went with it. Soon after getting back in the topic of sex came up, and if I would be mad if he and his gf have sex, saying he'd wear a condom. I told him I couldn't stop him. He began to tell me he had already lost his V-card and began to describe how amazing his older Gf was, especially in bed but never the part about the dildo. Erect I became again. He claimed that talking about even turned him on. I asked if he had turned out like his father, he claimed he didn't know so I stood up to show him and he sat in shock for a moment and then stood up to. My damn son was almost the same size and width, from there the topic of self pleasure came up and different was and he began to touch him self as I demonstrated each. I asked him if he felt awkward to which he stated he was very happy that we could be this close and I told him we could be as close as he wanted to be. My son startled me as he quickly grabbed my cock with his vice grip and took over jerking my cock. I didn't hesitate, I turned him around bent him over and began tonguing his asshole and stroking him. When I pushed my tongue in he moaned, and that got me going, so I slowly began to push my big cock tip into his little ass and from there it's history, I made my sons fantasy come true and drip from his ass.

Our father son relationship has greatly improved today.