Marnie came to him one day asking to "party" with their friends, which made him uncomfortable, but after sleeping on it, he came to the realization: YOLO (You only live once).
So when Marnie returned home, he agreed to do as she wished, with two of their friends present and eager to celebrate her birthday. He was admittedly nervous, but allowed his wife - who was possessed by Crowley at the time - to give the green light.
After the orgy, Crowley killed him and his friends. It is unknown what happened to Marnie.