I was 14yo, my sister was 16yo the summer she had an exchange student Lily from France staying with our family. My sister had already spent two weeks with the girl's family in spring, so it was her turn to stay with us. My dad and sister picked her up from the airport and when she arrived at our house it was 'love at first sight' for me! She was about 5' 7', slim build with brunette hair, but it was her legs and butt which really drew my attention. Wearing a short denim skirt, her slim and tanned legs seemed to go on and on, and her butt was real 'peachy' as they say.
The school had days out planned during her stay and as Ma and Pa were at work I spent most of those two weeks home alone. Having sneaked a peek up her skirt at her pale blue knickers as we all sat talking that first evening, I was keen to get a look at them again the following day when everyone had gone out. I snuck into my sisters rooms and found Lily's bags and had a look through. I eventually found her underwear, unused and clean-there were bikini style knickers, a couple of thongs and some silky ones too, but not the pale blue pair I had noticed the previous evening. Undeterred I grabbed a pair of purple silky knickers, took them to my room, wrapped them around my cock and began gently stroking. I pictured Lily in just her knickers and I soon felt that tingling feeling in my scrotum. Being careful not to cum in them I was soon pumping my hot man-milk over my stomach. Placing them back in her bag I was sated for the day.
On the second day after everyone had left I had a look through her bags again. Lily had seperated a bag just for her dirty laundry and there in the bottom were those pale blue knickers. I lifted them out and checked them over. Thinking she must have worn them two days they smelled of hot, girl pussy and my cock was stiff within seconds. Looking in the other bag for the silky ones I'd used the day before, they were not there and I guessed she must be wearing them. The thought alone got me even harder as I retreated to my room. With her smelly knickers under my nose I jerked my dribbling cock until I shot my load up to my chest.
To cut a long story short, over the two weeks I must have sniffed and licked at least a dozen of her dirty knickers, came in about half of them, and kept the first pair as a momento of a glorious period during that summer.