I grew up in a family with my 2 sisters, a brother and both my parents. I was the oldest and Rosalie was the youngest. We were all adopted. We had a good childhood though our parents being strong Catholics forbade many of the boy/girl interactions common to most teenagers. I was very immature socially and quite shy as a result.
As we grew up I was still the awkward nerd but Rosalie became an exceptionally attractive girl with to kill for legs and beautiful breasts. I had gone off to university and Rosalie was finishing grade 12. When I returned home on break I was astounded at how stunningly sexy she was and she knew it.
One evening she asked me to help her with some homework at the kitchen table. She was wearing a tube top with shorts. I sat down at the table and she came up behind me to look over my shoulder nestling my neck with her beautiful breasts. I felt my cock start to respond as she wiggled her breasts back and forth on my neck. She looked down at my lap and could see my hardon stretching out the loose fitting gym shorts I was wearing. Her grin almost caused me to come right there. She whispered in my ear that it would be so nice of me to just finish her homework. Like a good brother I complied. My mother was in the kitchen preparing supper at the time so when I was done it was going to be difficult to leave without my mother seeing my hardon. Rosalie reached down and gave my cock a quick squeeze before distracting mother by offering to help while I slipped out of the kitchen to the only bathroom in the house to relieve the pressure in my shorts.
I couldn't believe how lucky I was. I was so shy when approaching girls that I had never been close to getting laid and right beside me was a stunning babe who understood me and for a little help with home work who knows what might happen.
Later that evening Rosalie asked me if I wanted to play backgammon. My father was sitting in his chair while my mother sat on the couch. They were both watching tv and we set up the board on the floor. I was sitting cross-legged on one side and Rosalie sat legs spread on the other side. I had a hard time concentrating on the game as I could see some pubic hair poking out from the edge of her shorts. Rosalie had the darkest black hair on her head; full and luxurious. This preview of her pubes suggested that it would be the same. I lost the first game which was unusual and Rosalie commented with a sexy grin that now she knew how to win against me.
We went on to the next game and the head of my cock started to protrude from the hem of my gym shorts as I didn't have underwear on. Rosalie's eyes bulged and she licked her lips: only then did I realize what was happening. This realization caused my cock to grow and come further into the light.