From an early age my brother and I shared a room. He was 4 years older. When I was about 14, I noticed when he came home late at night, he would lie on his stomach, and put his pillow underneath him. I could then hear him pull down his underwear, and he would hump his pillow. He would start and stop, going quicker and quicker until he let out a muffled grunt. I would then hear him pull his underwear back up, and he would then fall quickly asleep.
Eventually, I understood what he was doing. One night, while listening and watching through the darkness, I too, put my pillow underneath me, and pulled my underwear down and humped my pillow. I kept up the pace with him, starting and stopping, going quicker and quicker, until we both made muffled grunts, and came together.
This went on for years, and I would wait up at night for him, hoping that it would be a jerk-off night. The sound of him putting his pillow underneath him and pulling down the band of his underwear, was almost enough for me to shoot my load, for I knew what was next. It was very exciting to hear him, and masturbate 'together.'
Keeping up his pace, and cumming at the same time was truly wonderful. I would make noises to let him know that I was doing the same thing he was; Getting bolder and louder, humping my pillow, as I would get closer to orgasm. After we came, the room would smell of cum. Sometimes, the next morning, while my brother showered, I would check out his pillow, and feel his dried cum on his pillow, and sniff the delicious smell of cum. I would also check out his underwear, which also would have dried cum, which would obviously ooze from his cock, after he slipped his underwear back on. The smell of cum and the feel of his dried cum, made me want to cum again. To this day, I love to smell my own dried cum on my cum rag the next morning.
My brother and I never spoke of our jerk off sessions, and he never let on that he knew. But he had to have!