This is a true account of my experience with my sister in law - she is 9 years older than me and should have known better!!
When I left the Navy and returned to my home town I realized I still had a thing for my sister-in-law. I used to go to the beach with her and my nieces and nephews on the off chance I would get a look at her tits and I found when she laid down, her bikini bottoms stretched across her hip bones and I could see her mound. To a horny young guy that was special!
As I needed some money, I started to baby-sit for my brother & sister-in-law. This gave me a chance to see her dressed up to go out -- my brother would sometimes cop a feel of her tits and make her nipples stick out like little thumbs. When the house was quiet I would look through her underwear and rub my cock with her knickers. One day I noticed a used pair of her knickers in the laundry basket in the bathroom - I sniffed the stained crotch and the smell was intoxicating -- I wanked off into them and stuffed them back into the basket.
After I got settled back at home I used to go out with them to the local clubs etc and this allowed me to dance with her. I always got a hard on and she never minded me grinding it into her as we swayed to the music. I'd also let my hands drop a bit so they were cupping her arse cheeks -- I always had to adjust myself before we parted!
I moved away up to London and shared a flat with a couple of other guys. We decided to have a party one weekend and I invited my brother and sister in law -- I would sleep in the lounge and they could have my bedroom. As the evening wore on I was getting randier and harder -- she was teasing and eventually she went to the loo. I waited outside the door and as she emerged I grabbed her and we fell into the bedroom next door -- we kissed -- not gentle but passionate, forcing our tongues into each others mouths. My hands roamed over her body, rubbing her tits and tracing her arse crack, pulling her into my hard on. She turned around, hiked her knickers to one side and I fucked her. Not slow and sensual as I'd always planned, but hard and forceful. I reached around her and squeezed and tugged at her tits as I pounded my 8 inches into her. It didn't last long -- I was young and in the heat of the moment. It didn't take too long before I exploded inside of her, I'd never come so hard. We quickly straightened our clothing and returned to the party -- no one was the wiser except us.