Unexpected Help

Several years ago my wife and I were camping with her sister and our brother-in-law. My wife had her period so it was up to me to take care of things. The girls were out hiking and I told my brother-in-law that I needed to drop a load. I started to jack off when he came over and asked if he could help. I didn't care at this point and let him stroke me. It felt so good having someone else do all the work! When I came it was a very powerful shot across the camper table. After I cleaned up the mess I asked him why he helped and he said that I had the biggest cock he had ever seen and wanted to stroke it and feel its length. It's an honest 8.25 inches when hard, and 5.5 inches around. His is about 5.5 inches long with a fat head. He had seen me naked before but never hard. We have jacked off together since then, but he has not offered to help again. I wouldn't mind the help!