A little out of hand

I'm a straight guy that likes to put toys in my ass occasionally when I masterbate it makes me cum so intensly.
This one time my wife had gone out for the day so I went up to our bedroom and got out some lube and a vibrating butt plug that has a few rings of rotating beads around the base it feels amazing so i lubed up my arsehole and layed on my side on the bed and slowly started to work it into my tight asshole gently until it almost went in then let it slide back out I played like this for a while in and out just to the thicker part of the toy teasing my ass with it until i just had to feel it filling me up, I pushed it in again just past the wider part an let my hole pull it the rest of the way in it felt amazing filling me up so I grabbed for the toys remote and turned on the rotating beads that are supposed to simulate a rim job but having never experienced one all I can say is they feel great then put the vibrations on and this really tops it off im in heaven so I roll onto my back and start stroking my 8 inch cock getting just to the point of cumming and stopping I did this a few times before turning up the speed of the rotating beads and vibrations, its then that I realised my 6 year old German shepard sam is sitting in the doorway watching and it startled the hell out of me so I stood up to shoo him away, as I did I felt the plug slipping out of my well lubed asshole and it popped out and clattered to the floor still vibrating and bounced under the dressing table I quickly turned and knelt down on all fours to grab it, when I was strached out ass in the air and head under the dressing table Sam suddenly mounted me from behind his 9 inch red rocket of a cock already out of its sheath and standing to attention now stabbing against my ass cheeks and around my hole within seconds of mounting me he found his target my already lubed up asshole I shouted out but it was too late in one motion he had impailed me to the ilt of his monster cock and with my head and shoulders under the dressing table and his full weight pressing down on my back I had nowhere to go he started pounding my ass relentlessly which started out painfull but after i had relaxed a bit started to feel really good right up until i could feel a large bulge trying to force itself into me and with every frenzied thrust from Sam managed to get inch by inch into my asshole until it popped in me completely and my hole closed tight around it I now had 9 inches of dog cock inside me and a large bulge that seemed to be swelling up even bigger, I couldnt stop myself I came in a massive explosion that soked the floor beneath me and left me breathless and shaking all over my body convulsing must have been the final straw for Sam as I felt him filling me up with cum wich set me off again and I shot my second load in under 5 minutes of each other making the puddle beneath be even bigger once my second orgasm had subsided I was stuck beneath Sam for another 20-30 minutes it didn't matter how hard I tried to push him off me he wouldn't move. Sam finally went soft enough to pull out of me and jumped down off of me and I collapsed into the puddle of my own cum and I felt some of sams cum leaking out of my ass and onto the floor sam hoped up onto the bed something he has never been aloud to do and started cleaning himself off, I finally managed to pull myself together enough to get up and went to get tissue to clean up the mess and have a shower still in complete shock at what had happened. Sam was asleep on the bed when my wife got home but she never found out about what had happened that day