As a guy who loves golden showers, and someone who has done them since I was a teen(gived and received) , I think I have figured out the psychology behind them. Keep in mind that I am not a psychologist and that these are just my observations and thoughts.
1.The most likely origin for this fetish is time we were kids at the urinals. Even before we were aware of the fact we are gay. It was the first time being surrounded by men with there dicks out, totally relaxed and natural, just doing what men do. So if aroused by these situation,like many of us where, this would be something that gets carved into our sexuality very deep. And that is why gay men are more likely to get into WS or just watching another guy take a leak then general population.
2.Is this guy experienced with WS or not. It's one thing to get turned on by something you see on porn,and completely different to actually do it.
So if he's a newbie you should probably take it step by step. Let him warm up to this new experience. Maybe start with some communal pissing, than pissing on his (or each others) body, than face, than mouth, and at the and drinking it. It can take anywhere from a few minutes to few sessions to get there.
