Go to the bathroom

You head inside and relieve yourself in the bathroom. As you head back down to the pool you pass by the door of Evan's little brother Billy. You peek inside and are shocked to find Billy is sprawled out on his back with his legs up in the air, getting fucked by Evan's father, Victor.

Your dick springs to attention as you stand in the hallway watching your friends younger brother getting his ass pounded by his father. Because you are drunk, you pull your dick out of your swimming shorts and start jerking off.

After a while you decide you maybe shouldn't be doing this, but as you go to pull up your shorts you accidentally hit the bedroom door with your arm and it swings open.

Both father and son stare at you standing in the doorway, Victor stopping his thrusting but leaving his dick deep in his son's ass. At first time seems to move slowly, but seeing your throbbing dick leaking massive amounts of precum onto the hallway floor, they smile at you, and Victor invites you over to the bed.

He pulls out of his son and guides your dick up to his son's ass, then pushes your butt so your dick enters. He pulls and pushes on your hips, helping you to fuck his son. Soon your fucking Billy on your own accord, his father watching and jerking his throbbing member. "Yes! That's a good boy. Fuck my son!" This causes you to cum inside Billy's ass.

Seeing your cum start to flow out of his son's ass sends Victor over the edge and he sprays you and his son with his massive load.

You are about to pull up your shorts and leave, but Victor stops you. "Not so fast," he says. "It's my turn."

Billy pulls you onto the bed and presses your dicks together, and Victor climbs on top and slides his ass over both your dicks, riding up and down, grinding your and Billy's dicks together.