Ron had invited me to his family's summer house in up state New York.
We shared a room that had two single beds and had an attached enclosed porch area.
At this time I was a two to three times a day masturbator with four or five times not being uncommon. Unfortunately I had zero privacy while staying here and the place only had one bathroom and I felt too weird to do it in the same place his mom took a bath.
It was the night of the third day there. Ron and I were lying in our respective beds chatting about this and that. My dick was rock hard and I was slowly stroking it through my underwear. I had massive pre cum back then and the wet spot on my briefs was getting bigger by the minute.
Ron asked if I wanted to finish the baseball board game that we had started earlier. I agreed but told him I wasn't getting dressed. I got out of bed with my obviously hard dick straining through my white briefs and walked the few feet into the porch area. Ron followed a second later but had put on some pajama shorts.
We played the game while I sat there with my boner and my wet spot, waiting for Ron to say something, but he never did. We finished the game and Ron went back into the room and layed on his bed. I knew I had to cum so with Ron literally a few feet away but around the corner I stuck my hand down my briefs and started stroking. I was so wet and slippery that I knew I wasn't going to last long. I was on my 10th or 11th stroke when Ron asked me what I was doing, I think I grunted out 'nothing' as I shot my three day load into my briefs.
I got up to enter the room when I noticed the full length mirror that was hanging on the door entering the porch area. Ron was lying on his stomach looking in the mirror. He had seen the whole thing!
I excused myself and went to the bathroom to clean up. When I came back he didn't say word about it.